AT21CS01/AT21CS11
Single-Wire, I/O Powered 1-Kbit (128 x 8) Serial EEPROM
with a Unique, Factory-Programmed 64-Bit Serial Number
Features
• Low‑Voltage Operation:
– AT21CS01 is self-powered via the 1.7V to 3.6V pull‑up voltage on the SI/O line
– AT21CS11 is self-powered via the 2.7V to 4.5V pull‑up voltage on the SI/O line
• Internally Organized as 128 Words of Eight Bits Each (1-Kbit)
• Single-Wire Serial Interface with I2C Protocol Structure:
– Device communication is achieved through a single I/O pin
• Standard Speed and High-Speed Mode Options:
– 15.4 kbps maximum bit rate in Standard Speed mode (AT21CS01 only)
– 125 kbps maximum bit rate in High-Speed mode (AT21CS01 and AT21CS11)
• 8‑Byte Page Write or Single Byte Writes Allowed
• Discovery Response Feature for Quick Detection of Devices on the Bus
• ROM Zone Support:
– Device is segmented into four 256‑bit zones, each of which can be permanently made
read‑only (ROM)
• 256‑bit Security Register:
– Lower eight bytes contains a factory-programmed, read-only, 64‑bit serial number that is
unique to all Microchip single‑wire products
– Next eight bytes are reserved for future use and will read FFh
– Upper 16 bytes are user‑programmable and permanently lockable
• Self‑Timed Write Cycle (5 ms maximum)
• Manufacturer Identification Register:
– Device responds with unique value for Microchip as well as density and revision information
• High Reliability:
– Endurance: 1,000,000 write cycles
– Data retention: 100 years
– IEC 61000-4-2 Level 4 ESD Compliant (±8 kV Contact, ±15 kV Air Discharge)
• Green (Lead-free/Halide-free/RoHS Compliant) Package Options
• Die Sale Options in Wafer Form and Tape and Reel
Packages
2-pad XSFN, 3-lead SOT23, 8-lead SOIC and 4-ball thin WLCSP.
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 1
Package Types (not to scale)
8-lead SOIC
(Top View)
NC 1
2
3
4
8
7
6
5
NC
NC
GND
NC
NC
NC
SI/O
SI/O
GND
4-ball WLCSP
(Top View)
NC
NC
A1 A2
B1
B2
3
2
1
GND
SI/O
NC
3-lead SOT23
(Top View)
SI/O
GND
1
2
2-pad XSFN
(Top View)
Description
The AT21CS01/11 is a 2-pin memory (SI/O signal and Ground) that harvests energy from the signal pin to
power the integrated circuit. It provides 1,024 bits of Serial Electrically Erasable and Programmable Read-
Only Memory (SEEPROM) organized as 128 words of eight bits each.
The device is optimized to add configuration and use information in unpowered attachments using a two-point
mechanical connection that brings only one signal (SI/O) and GND to the unpowered attachment. Some
unpowered attachment application examples include analog sensor calibration data storage, ink and toner
printer cartridge identification, and management of after‑market consumables. The device’s software
addressing scheme allows up to eight devices to share a common single‑wire bus. The device is available in
space‑saving package options and operates with an external pull‑up voltage from 1.7V to 3.6V on the SI/O
line (AT21CS01) or from 2.7V to 4.5V on the SI/O line (AT21CS11).
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 2
System Configuration Using Single-Wire Serial EEPROMs
Bus Master:
Microcontroller
Slave 0
AT21CSXX
GND
VCC
GND
SI/O
RPUP
(See Sections 1.3 and 1.4 for requirements.)
VPUP
SI/O
Slave 1
AT21CSXX
GND
SI/O
Slave 7
AT21CSXX
GND
SI/O
Block Diagram
1 page
Internal
Timing
Generation
GND
Memory
System Control
Module
High Voltage
Generation Circuit
Data & ACK
Input/Output Control
Command
Control
Reset
Detection
DOUT
DIN
Device
Configuration
Latches
SI/O
Device
Power
Extraction
EEPROM Array
Column Decoder
Row Decoder
Data Register
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 3
Table of Contents
Features.......................................................................................................................... 1
Packages.........................................................................................................................1
Package Types (not to scale).......................................................................................... 2
Description.......................................................................................................................2
System Configuration Using Single-Wire Serial EEPROMs............................................3
Block Diagram................................................................................................................. 3
1. Electrical Characteristics........................................................................................... 6
1.1. Absolute Maximum Ratings(1)...................................................................................................... 6
1.2. AT21CS01/11 DC and AC Operating Range................................................................................6
1.3. AT21CS01 DC Characteristics(1)..................................................................................................6
1.4. AT21CS11 DC Characteristics(1).................................................................................................. 7
1.5. AT21CS01/11 AC Characteristics.................................................................................................8
2. Pin Descriptions.......................................................................................................11
2.1. No Connect.................................................................................................................................11
2.2. Serial Input and Output...............................................................................................................11
3. Device Operation and Communication....................................................................12
3.1. Single-Wire Bus Transactions.................................................................................................... 12
4. Device Addressing and I2C Protocol Emulation...................................................... 18
4.1. Memory Organization................................................................................................................. 18
5. Available Opcodes...................................................................................................20
5.1. EEPROM Access (Opcode Ah)..................................................................................................20
5.2. Security Register Access (Opcode Bh)...................................................................................... 20
5.3. Lock Security Register (Opcode 2h).......................................................................................... 20
5.4. ROM Zone Register Access (Opcode 7h)..................................................................................20
5.5. Freeze ROM Zone State (Opcode 1h)....................................................................................... 21
5.6. Manufacturer ID Read (Opcode Ch).......................................................................................... 21
5.7. Standard Speed Mode (Opcode Dh)..........................................................................................21
5.8. High-Speed Mode (Opcode Eh)................................................................................................. 21
6. Write Operations......................................................................................................22
6.1. Device Behavior During Internal Write Cycle............................................................................. 22
6.2. Byte Write...................................................................................................................................22
6.3. Page Write..................................................................................................................................23
6.4. Writing to the Security Register..................................................................................................23
6.5. Locking the Security Register.....................................................................................................24
6.6. Setting the Device Speed...........................................................................................................25
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 4
7. Read Operations..................................................................................................... 27
7.1. Current Address Read within the EEPROM...............................................................................27
7.2. Random Read within the EEPROM........................................................................................... 28
7.3. Sequential Read within the EEPROM........................................................................................ 28
7.4. Read Operations in the Security Register.................................................................................. 29
7.5. Manufacturer ID Read................................................................................................................30
8. ROM Zones............................................................................................................. 32
8.1. ROM Zone Size and ROM Zone Registers................................................................................ 32
8.2. Programming and Reading the ROM Zone Registers................................................................32
8.3. Device Response to a Write Command Within an Enabled ROM Zone.................................... 34
9. Device Default Condition from Microchip................................................................ 36
10. Packaging Information.............................................................................................37
10.1. Package Marking Information.....................................................................................................37
11. Revision History.......................................................................................................42
The Microchip Web Site................................................................................................ 43
Customer Change Notification Service..........................................................................43
Customer Support......................................................................................................... 43
Product Identification System........................................................................................44
Microchip Devices Code Protection Feature................................................................. 45
Legal Notice...................................................................................................................45
Trademarks................................................................................................................... 45
Quality Management System Certified by DNV.............................................................46
Worldwide Sales and Service........................................................................................47
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 5
1. Electrical Characteristics
1.1 Absolute Maximum Ratings(1)
Temperature under bias -55°C to +125°C
Storage temperature -65°C to +150°C
Voltage on any pin with respect to ground -0.6V to VPUP +0.5V
DC output current 15.0 mA
Note:
1. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to
the device. This is a stress rating only and functional operation of the device at these or any other
conditions beyond those indicated in the operational sections of this specification are not implied.
Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
1.2 AT21CS01/11 DC and AC Operating Range
AT21CS01 AT21CS11
Operating Temperature (Case) Industrial Temperature Range -40°C to +85°C -40°C to +85°C
VPUP Voltage tied to SI/O Voltage Range 1.7V to 3.6V 2.7V to 4.5V
1.3 AT21CS01 DC Characteristics(1)
Parameter Symbol Minimum Typical(2)Maximum Units Test Conditions
Pull-up Voltage VPUP 1.7 — 3.6 V High-Speed
mode
2.7 — 3.6 V Standard Speed
mode
Pull-up Resistance RPUP 130 — 200 Ω VPUP = 1.7V
0.2 — 1.8 kΩ VPUP = 2.7V
0.33 — 4 kΩ VPUP = 3.6V
Active Current, Read IA1 — 0.08 0.3 mA VPUP = 3.6V;
SI/O = VPUP
Active Current, Write IA2 — 0.20 0.5 mA VPUP = 3.6V
Standby Current ISB — 0.6 1.5 µA VPUP = 1.8V(3);
SI/O = VPUP
— 0.7 2.5 µA VPUP = 3.6V
Input Low Level(3)(4)VIL –0.6 — 0.5 V
Input High Level(3)(4)VIH VPUP x 0.7 — VPUP + 0.5 V
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 6
Parameter Symbol Minimum Typical(2)Maximum Units Test Conditions
SI/O Hysteresis(3)(4)(5)VHYS 0.128 — 1.17 V
Output Low Level VOL 0 — 0.4 V IOL = 4 mA
Bus Capacitance CBUS — — 1000 pF
Note:
1. Parameters are applicable over the operating range in AT21CS01/11 DC and AC Operating Range,
unless otherwise noted.
2. Typical values characterized at TA = +25°C unless otherwise noted.
3. This parameter is characterized but is not 100% tested in production.
4. VIH, VIL, and VHYS are a function of the internal supply voltage, which is a function of VPUP, RPUP,
CBUS, and timing used. Use of a lower VPUP, higher RPUP, higher CBUS, and shorter tRCV creates
lower VIH, VIL and VHYS values.
5. Once VIH is crossed on a rising edge of SI/O, the voltage on SI/O must drop at least by VHYS to be
detected as a logic ‘0’.
1.4 AT21CS11 DC Characteristics(1)
Parameter Symbol Minimum Typical(2)Maximum Units Test Conditions
Pull-up Voltage VPUP 2.7 — 4.5 V High-Speed
mode
Pull-up Resistance RPUP 0.2 — 1.8 kΩ VPUP = 2.7V
0.4 — 5.4 kΩ VPUP = 4.5V
Active Current, Read IA1 — 0.08 0.3 mA VPUP = 4.5V;
SI/O = VPUP
Active Current, Write IA2 — 0.20 0.5 mA VPUP = 4.5V
Standby Current ISB — 0.6 1.5 µA VPUP = 2.7V(3);
SI/O = VPUP
— 0.7 3.0 µA VPUP = 4.5V;
SI/O = VPUP
Input Low Level(3)(4)VIL –0.6 — 0.5 V
Input High Level(3)(4)VIH VPUP x 0.7 — VPUP + 0.5 V
SI/O Hysteresis(3)(4)(5)VHYS 0.128 — 1.4 V
Output Low Level VOL 0 — 0.4 V IOL = 4 mA
Bus Capacitance CBUS — — 1000 pF
Note:
1. Parameters are applicable over the operating range in AT21CS01/11 DC and AC Operating Range,
unless otherwise noted.
2. Typical values characterized at TA = +25°C unless otherwise noted.
3. This parameter is characterized but is not 100% tested in production.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 7
4. VIH, VIL, and VHYS are a function of the internal supply voltage, which is a function of VPUP, RPUP,
CBUS, and timing used. Use of a lower VPUP, higher RPUP, higher CBUS, and shorter tRCV creates
lower VIH, VIL and VHYS values.
5. Once VIH is crossed on a rising edge of SI/O, the voltage on SI/O must drop at least by VHYS to be
detected as a logic ‘0’.
1.5 AT21CS01/11 AC Characteristics
1.5.1 Reset and Discovery Response Timing
Parameter and Condition(1)(2)Symbol Standard
Speed(3)(4)
High Speed Units
Min. Max. Min. Max.
Reset Low Time, Device in Inactive
State
tRESET 480 — 48 — µs
Discharge Low Time, Device in Active
Write Cycle (tWR)
tDSCHG 150 — 150 — µs
Reset Recovery Time tRRT N/A N/A 8 — µs
Discovery Response Request tDRR N/A N/A 1 2 - tPUP(5)µs
Discovery Response Acknowledge
Time
tDACK N/A N/A 8 24 µs
Master Strobe Discovery Response
Time
tMSDR N/A N/A 2 6 µs
SI/O High Time for Start/Stop
Condition
tHTSS N/A N/A 150 — µs
Note:
1. Parameters applicable over operating range in AT21CS01/11 DC and AC Operating Range, unless
otherwise noted.
2. AC measurement conditions for the table above:
– Loading capacitance on SI/O: 100 pF
– RPUP (bus line pull-up resistor to VPUP): 1 kΩ; VPUP: 2.7V
3. Due to the fact that the device will default to High-Speed mode upon Reset, the Reset and
Discovery Response Timing after tRESET does not apply for Standard Speed mode. High-Speed
mode timing applies in all cases after tRESET.
4. Standard Speed is not available on the AT21CS11.
5. tPUP is the time required once the SI/O line is released to be pulled up from VIL to VIH. This value is
application specific and is a function of the loading capacitance on the SI/O line as well as the RPUP
chosen. Limits for these values are provided in AT21CS01 DC Characteristics(1) and AT21CS11
DC Characteristics(1).
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 8
1.5.2 Data Communication Timing
Parameter and Condition(1)(2)Symbol Frame Type Standard
Speed(3)
High Speed Units
Min. Max. Min. Max.
Bit Frame Duration tBIT Input and
Output Bit
Frame
40 100 tLOW0 +
tPUP(4) +
tRCV
25 µs
SI/O High Time for Start/Stop
Condition
tHTSS Input Bit
Frame
600 — 150 — µs
SI/O Low Time, Logic ‘0’
Condition
tLOW0 Input Bit
Frame
24 64 6 16 µs
SI/O Low Time, Logic ‘1’
Condition
tLOW1 Input Bit
Frame
4 8 1 2 µs
Master SI/O Low Time During
Read
tRD Output Bit
Frame
4 8 -
tPUP(4)
1 2 -
tPUP(4)
µs
Master Read Strobe Time tMRS Output Bit
Frame
tRD +
tPUP(4)
8 tRD +
tPUP(4)
2 µs
Data Output Hold Time (Logic
‘0’)
tHLD0 Output Bit
Frame
8 24 2 6 µs
Slave Recovery Time tRCV Input and
Output Bit
Frame
8 — 2(5)— µs
Noise Filtering Capability on
SI/O
tNOISE Input Bit
Frame
0.5 — — — µs
Note:
1. Parameters applicable over operating range in AT21CS01/11 DC and AC Operating Range, unless
otherwise noted.
2. AC measurement conditions for the table above:
– Loading capacitance on SI/O: 100 pF
– RPUP (bus line pull-up resistor to VPUP): 1 kΩ; VPUP: 2.7V
3. Standard Speed is not available on the AT21CS11.
4. tPUP is the time required once the SI/O line is released to be pulled up from VIL to VIH. This value is
application specific and is a function of the loading capacitance on the SI/O line as well as the RPUP
chosen. Limits for these values are provided in AT21CS01 DC Characteristics(1).
5. The system designer must select an combination of RPUP, CBUS, and tBIT such that the minimum
tRCV is satisfied. The relationship of tRCV within the bit frame can be expressed by the following
formula: tBIT = tLOW0 + tPUP + tRCV.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 9
1.5.3 EEPROM Cell Performance Characteristics
Operation Min. Max. Units Test Condition
Write Cycle Time
(tWR)
— 5 ms VPUP (min.) < VPUP < VPUP (max.),
TA = 25°C, Byte or Page Write mode
Write Endurance(1)1,000,000 — Write Cycles VPUP (min.) < VPUP < VPUP (max.),
TA = 25°C, Byte or Page Write mode
Data Retention(2)100 — Years VPUP (min.) < VPUP < VPUP (max.),
TA = 55°C
Note:
1. Write endurance performance is determined through characterization and the qualification process.
2. The data retention capability is determined through qualification and checked on each device in
production.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 10
2. Pin Descriptions
The descriptions of the pins are listed in Table 2-1.
Table 2-1. Pin Function Table
Name 2-pad XSFN 3-lead SOT23 8-lead SOIC 4-ball WLCSP Function
NC — — 1 — No Connect
NC — — 2 — No Connect
NC — 2 3 — No Connect
GND 2 3 4 B1 Ground
SI/O 1 1 5 A1 Serial Input and
Output
NC — — 6 No Connect
NC — — 7 — No Connect
NC — — 8 — No Connect
2.1 No Connect
The NC pins are not internally connected. These pins can be connected to GND or left floating.
2.2 Serial Input and Output
The SI/O pin is an open-drain, bidirectional input/output pin used to serially transfer data to and from the
device.
The SI/O pin must be pulled high using an external pull‑up resistor (not to exceed 4 kΩ in value) and may
be wire-ORed with any number of other open‑drain or open‑collector pins from other devices on the same
bus.
The device also uses the SI/O pin as its voltage source by drawing and storing power during the periods
that the pin is pulled high to a voltage level between 1.7V and 3.6V (AT21CS01) and between 2.7V and
4.5V (AT21CS11).
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 11
3. Device Operation and Communication
The AT21CS01/11 operates as a slave device and utilizes a single‑wire digital serial interface to
communicate with a host controller, commonly referred to as the bus master. The master controls all read
and write operations to the slave devices on the serial bus. The device has two speeds of operation,
Standard Speed mode (AT21CS01) and High-Speed mode (AT21CS01 and AT21CS11).
The device utilizes an 8-bit data structure. Data is transferred to and from the device via the single‑wire
serial interface using the Serial Input/Output (SI/O) pin. Power to the device is also provided via the SI/O
pin, thus only the SI/O pin and the GND pin are required for device operation. Data sent to the device
over the single‑wire bus is interpreted by the state of the SI/O pin during specific time intervals or slots.
Each time slot is referred to as a bit frame and lasts tBIT in duration. The master initiates all bit frames by
driving the SI/O line low. All commands and data information are transferred with the Most Significant bit
(MSb) first.
The software sequence sent to the device is an emulation of what would be sent to an I2C Serial
EEPROM with the exception that typical 4-bit device type identifier of 1010b in the device address is
replaced by a 4-bit opcode. The device has been architected in this way to allow for rapid deployment
and significant reuse of existing I2C firmware. For more details about the way the device operates, refer
to Device Addressing and I2C Protocol Emulation .
During bus communication, one data bit is transmitted in every bit frame, and after eight bits (one byte) of
data has been transferred, the receiving device must respond with either an acknowledge (ACK) or a
no-acknowledge (NACK) response bit during a ninth bit window. There are no unused clock cycles during
any read or write operation, so there must not be any interruptions or breaks in the data stream during
each data byte transfer and ACK or NACK clock cycle. In the event where an unavoidable system
interrupt is required, refer to the requirements outlined in Communication Interruptions.
3.1 Single-Wire Bus Transactions
Types of data transmitted over the SI/O line:
• Reset and Discovery Response
• Logic ‘0’ or Acknowledge (ACK)
• Logic ‘1’ or No Acknowledge (NACK)
• Start Condition
• Stop Condition
The Reset and Discovery Response is not considered to be part of the data stream to the device,
whereas the remaining four transactions are all required in order to send data to and receive data from
the device. The difference between the different types of data stream transactions is the duration that
SI/O is driven low within the bit frame.
3.1.1 Device Reset/Power-up and Discovery Response
3.1.1.1 Resetting the Device
A Reset and Discovery Response sequence is used by the master to reset the device as well as to
perform a general bus call to determine if any devices are present on the bus.
To begin the Reset portion of the sequence, the master must drive SI/O low for a minimum time. If the
device is not currently busy with other operations, the master can drive SI/O low for a time of tRESET. The
length of tRESET differs for Standard Speed mode and for High-Speed mode.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 12
However, if the device is busy, the master must drive SI/O for a longer time of tDSCHG to ensure the device
is reset as discussed in Interrupting the Device during an Active Operation. The Reset time forces any
internal charge storage within the device to be consumed, causing the device to lose all remaining
standby power available internally.
Upon SI/O being released for a sufficient amount of time to allow the device time to power-up and
initialize, the master must then always request a Discovery Response Acknowledge from the
AT21CS01/11 prior to any commands being sent to the device. The master can then determine if an
AT21CS01/11 is present by sampling for the Discovery Response Acknowledge from the device.
3.1.1.2 Device Response Upon Reset or Power-Up
After the device has been powered up or after the master has reset the device by holding the SI/O line
low for tRESET or tDSCHG, the master must then release the line which will be pulled high by an external
pull-up resistor. The master must then wait an additional minimum time of tRRT before the master can
request a Discovery Response Acknowledge from the device.
The Discovery Response Acknowledge sequence begins by the master driving the SI/O line low which
will start the AT21CS01/11 internal timing circuits. The master must continue to drive the line low for tDRR.
During the tDRR time, the AT21CS01/11 will respond by concurrently driving SI/O low. The device will
continue to drive SI/O low for a total time of tDACK. The master should sample the state of the SI/O line at
tMSDR past the initiation of tDRR. By definition, the tDACK minimum is longer than the tMSDR maximum time,
thereby ensuring the master can always correctly sample the SI/O for a level less than VIL. After the tDACK
time has elapsed, the AT21CS01/11 will release SI/O which will then be pulled high by the external
pull‑up resistor.
The master must then wait tHTSS to create a Start condition before continuing with the first command (see
Start/Stop Condition for more details about Start conditions). By default, the device will come out of Reset
in High-Speed mode. Changing the device to Standard Speed mode is covered in Standard Speed Mode
(Opcode Dh). The AT21CS01/11 will power-up with its internal Address Pointer set to zero.
The timing requirements for the Reset and Discovery Response sequence for both Standard Speed and
High-Speed mode can be found in AT21CS01/11 AC Characteristics.
3.1.2 Interrupting the Device during an Active Operation
To conserve the stored energy within the onboard parasitic power system and minimize overall active
current, the AT21CS01/11 will not monitor the SI/O line for new commands while it is busy executing a
previously sent command. As a result, the device is not able to sense how long SI/O has been in a given
state. If the master requires to interrupt the device during an active operation, it must drive SI/O low long
enough to deplete all of its remaining stored power. This time is defined as tDSCHG, after which a normal
Discovery Response can begin by releasing the SI/O line.
Figure 3-1. Reset and Discovery Response Waveform
SI/O
tRESET / tDSCHG
VIL
VIH
MASTER PULL-UP RESISTORAT21CS01
Begin Next
Command with
Start Condition
tRRT
tDACK
tMSDR
Master
Sampling
Window
tDRR
tPUP
tHTSS
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 13
3.1.3 Data Input and Output Bit Frames
Communication with the AT21CS01/11 is conducted in time intervals referred to as a bit frame and lasts
tBIT in duration. Each bit frame contains a single binary data value. Input bit frames are used to transmit
data from the master to the AT21CS01/11 and can either be a logic ‘0’ or a logic ‘1’. An output bit frame
carries data from the AT21CS01/11 to the master. In all input and output cases, the master initiates the bit
frame by driving the SI/O line low. Once the AT21CS01/11 detects the SI/O being driven below the VIL
level, its internal timing circuits begin to run.
The duration of each bit frame is allowed to vary from bit to bit as long as the variation does not cause the
tBIT length to exceed the specified minimum and maximum values (see AT21CS01/11 AC
Characteristics). The tBIT requirements will vary depending on whether the device is set for Low-Speed or
High-Speed mode. For more information about setting the speed of the device, refer to Setting the Device
Speed.
3.1.3.1 Data Input Bit Frames
A data input bit frame can be used by the master to transmit either a logic ‘0’ or logic ‘1’ data bit to the
AT21CS01/11. The input bit frame is initiated when the master drives the SI/O line low. The length of time
that the SI/O line is held low will dictate whether the master is transmitting a logic ‘0’ or a logic ‘1’ for that
bit frame. For a logic ‘0’ input, the length of time that the SI/O line must be held low is defined as tLOW0.
Similarly, for a logic ‘1’ input, the length of time that the SI/O line must be held low is defined as tLOW1.
The AT21CS01/11 will sample the state of the SI/O line after the maximum tLOW1 but prior to the minimum
tLOW0 after SI/O was driven below the VIL threshold to determine if the data input is a logic ‘0’ or a
logic ‘1’. If the master is still driving the line low at the sample time, the AT21CS01/11 will decode that bit
frame as a logic ‘0’ as SI/O will be at a voltage less than VIL. If the master has already released the SI/O
line, the AT21CS01/11 will see a voltage level greater than or equal to VIH because of the external pull-up
resistor, and that bit frame will be decoded as a logic ‘1’. The timing requirements for these parameters
can be found in AT21CS01/11 AC Characteristics.
A logic ‘0’ condition has multiple uses in the I2C emulation sequences. It is used to signify a ‘0’ data bit,
and it also is used for an Acknowledge (ACK) response. Additionally, a logic ‘1’ condition is also is used
for a No Acknowledge (NACK) response in addition to the nominal ‘1‘ data bit.
Figure 3-2 and Figure 3-3 depict the logic ‘0’ and logic ‘1’ input bit frames.
Figure 3-2. Logic 0 Input Condition Waveform
SI/O
tLOW0
VIL
VIH
tBIT
MASTER PULL-UP RESISTOR
tRCV
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 14
Figure 3-3. Logic 1 Input Condition Waveform
SI/O
tLOW1
VIL
VIH
tBIT
MASTER PULL-UP RESISTOR
3.1.3.2 Start/Stop Condition
All transactions to the AT21CS01/11 begin with a Start condition; therefore, a Start can only be
transmitted by the master to the slave. Likewise, all transactions are terminated with a Stop condition and
thus a Stop condition can only be transmitted by the master to the slave.
The Start and Stop conditions require identical biasing of the SI/O line. The Start/Stop condition is
created by holding the SI/O line at a voltage of VPUP for a duration of tHTSS. Refer to AT21CS01/11 AC
Characteristics for timing minimums and maximums.
Figure 3-4 and Figure 3-5 depict the Start and Stop conditions.
Figure 3-4. Start Condition Waveform
SI/O
VIL
VIH
tHTSS
MASTER PULL-UP RESISTOR
Figure 3-5. Stop Condition Waveform
SI/O
VIL
VIH
tHTSS
MASTER PULL-UP RESISTOR
Previous
Bit Frame tRCV
3.1.3.3 Communication Interruptions
In the event that a protocol sequence is interrupted midstream, this sequence can be resumed at the
point of interruption if the elapsed time of inactivity (where SI/O is idle) is less that the maximum tBIT time.
The maximum allowed value will differ if the device is High-Speed mode or Low-Speed mode (see Setting
the Device Speed).
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 15
Note: The interruption of protocol must not occur during a write sequence immediately after a logic ‘0’
“ACK” response when sending data to be written to the device. In this case, the interruption will be
interpreted as a Stop condition and will cause an internal write cycle to begin. The device will be busy for
tWR time and will not respond to any commands.
Note: For systems that cannot accurately monitor the location of interrupts, it is recommended to ensure
that a minimum interruption time be observed consistent with the longest busy operation of the device
(tWR). Communicating with the device while it is in an internal write cycle by the master driving SI/O low
could cause the byte(s) being written to become corrupted and must be avoided. The behavior of the
device during a write cycle is described in more detail in Device Behavior During Internal Write Cycle.
If the sequence is interrupted for longer than the maximum tBIT, the master must wait at least the
minimum tHTSS before continuing. By waiting the minimum tHTSS time, a new Start condition is created
and the device is ready to receive a new command. It is recommended that the master start over and
repeat the transaction that was interrupted midstream.
3.1.3.4 Data Output Bit Frame
A data output bit frame is used when the master is to receive communication back from the
AT21CS01/11. Data output bit frames are used when reading any data out as well as any ACK or NACK
responses from the device. Just as in the input bit frame, the master initiates the sequence by driving the
SI/O line below the VIL threshold which engages the AT21CS01/11 internal timing generation circuit.
Within the output bit frame is the critical timing parameter tRD, which is defined as the amount of time the
master must continue to drive the SI/O line low after crossing the below VIL threshold to request a data bit
back from the AT21CS01/11. Once the tRD duration has expired, the master must release the SI/O line.
If the AT21CS01/11 is responding with a logic ‘0’ (for either a ‘0’ data bit or an ACK response), it will begin
to pull the SI/O line low concurrently during the tRD window and continue to hold it low for a duration of
tHLD0, after which it will release the line to be pulled back up to VPUP (see Figure 3-6). Thus, when the
master samples SI/O within the tMRS window, it will see a voltage less than VIL and decode this event as a
logic ’0’. By definition, the tHLD0 time is longer than the tMRS time and therefore, the master is ensured to
sample while the AT21CS01/11 is still driving the SI/O line low.
Figure 3-6. Logic 0 Data Output Bit Frame Waveform
AT21CS01 [DATASHEET]
Atmel-8903A-SEEPROM-AT21CS01-Datasheet_082015
10
3.1.3.4 Data Output Bit Frame
A data output Bit Frame is used when the Master is to receive communication back from the AT21CS01. Data
output Bit Frames are used when reading any data out as well as any ACK or NACK responses from the device.
Just as in the input Bit Frame, the Master initiates the sequence by driving the SI/O line below the VIL threshold
which engages the AT21CS01’s internal timing generation circuit.
Within the output Bit Frame is the critical timing parameter tRD, which is defined as the amount of time the
Master must continue to drive the SI/O line low after crossing the below VIL threshold to request a data bit back
from the AT21CS01. Once the tRD duration has expired, the Master must release the SI/O line.
If the AT21CS01 is responding with a Logic 0 (for either a ‘0’data bit or an ACK response), it will begin to pull
the SI/O line low concurrently during the tRD window and continue to hold it low for a duration of tHLD0, after
which it will release the line to be pulled back up to VPUP (see Figure 3-6). Thus, when the Master samples SI/O
within the tMRS window, it will see a voltage less than VIL and decode this event as a Logic 0. By definition, the
tHLD0 time is longer than the tMRS time and therefore the Master is guaranteed to sample while the AT21CS01 is
still driving the SI/O line low.
Figure 3-6. Logic 0 Data Output Bit Frame Waveform
If the AT21CS01 intends to respond with a Logic 1 (for either a ‘1’data bit or a NACK response), it will not drive
the SI/O line low at all. Once the Master releases the SI/O line after the maximum tRD has elapsed, the line will
be pulled up to VPUP. Thus when the Master samples the SI/O line within the tMRS window, it will detect a voltage
greater than VIH and decode this event as a Logic 1.
The data output Bit Frame is shown in greater detail below in Figure 3-7.
Figure 3-7. Logic 1 Data Output Bit Frame Waveform
SI/O
VIL
VIH
t
BIT
MASTER PULL-UP RESISTOR
t
MRS
t
RCV
AT21CS01
Master
Sampling
Window
t
RD
t
HLD0
t
PUP
SI/O
V
IL
V
IH
t
BIT
MASTER PULL-UP RESISTOR
t
MRS
AT21CS01
Master
Sampling
Window
t
RD
t
PUP
Note: AT21CS01 will not drive the SI/O line during a Logic 1 output Bit Frame.
If the AT21CS01/11 intends to respond with a logic ‘1’ (for either a ‘1’ data bit or a NACK response), it will
not drive the SI/O line low at all. Once the master releases the SI/O line after the maximum tRD has
elapsed, the line will be pulled up to VPUP. Thus, when the master samples the SI/O line within the tMRS
window, it will detect a voltage greater than VIH and decode this event as a logic ‘1’.
The data output bit frame is shown in greater detail below in Figure 3-7.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 16
Figure 3-7. Logic 1 Data Output Bit Frame Waveform
AT21CS01 [DATASHEET]
Atmel-8903A-SEEPROM-AT21CS01-Datasheet_082015
10
3.1.3.4 Data Output Bit Frame
A data output Bit Frame is used when the Master is to receive communication back from the AT21CS01. Data
output Bit Frames are used when reading any data out as well as any ACK or NACK responses from the device.
Just as in the input Bit Frame, the Master initiates the sequence by driving the SI/O line below the VIL threshold
which engages the AT21CS01’s internal timing generation circuit.
Within the output Bit Frame is the critical timing parameter tRD, which is defined as the amount of time the
Master must continue to drive the SI/O line low after crossing the below VIL threshold to request a data bit back
from the AT21CS01. Once the tRD duration has expired, the Master must release the SI/O line.
If the AT21CS01 is responding with a Logic 0 (for either a ‘0’data bit or an ACK response), it will begin to pull
the SI/O line low concurrently during the tRD window and continue to hold it low for a duration of tHLD0, after
which it will release the line to be pulled back up to VPUP (see Figure 3-6). Thus, when the Master samples SI/O
within the tMRS window, it will see a voltage less than VIL and decode this event as a Logic 0. By definition, the
tHLD0 time is longer than the tMRS time and therefore the Master is guaranteed to sample while the AT21CS01 is
still driving the SI/O line low.
Figure 3-6. Logic 0 Data Output Bit Frame Waveform
If the AT21CS01 intends to respond with a Logic 1 (for either a ‘1’data bit or a NACK response), it will not drive
the SI/O line low at all. Once the Master releases the SI/O line after the maximum tRD has elapsed, the line will
be pulled up to VPUP. Thus when the Master samples the SI/O line within the tMRS window, it will detect a voltage
greater than VIH and decode this event as a Logic 1.
The data output Bit Frame is shown in greater detail below in Figure 3-7.
Figure 3-7. Logic 1 Data Output Bit Frame Waveform
SI/O
VIL
VIH
t
BIT
MASTER PULL-UP RESISTOR
t
MRS
t
RCV
AT21CS01
Master
Sampling
Window
t
RD
t
HLD0
t
PUP
SI/O
V
IL
V
IH
t
BIT
MASTER PULL-UP RESISTOR
t
MRS
AT21CS01
Master
Sampling
Window
t
RD
t
PUP
Note: AT21CS01 will not drive the SI/O line during a Logic 1 output Bit Frame.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 17
4. Device Addressing and I2C Protocol Emulation
Accessing the device requires a Start condition followed by an 8-bit device address word.
The AT21CS01/11 protocol sequence emulates what would be required for an I2C Serial EEPROM, with
the exception that the beginning four bits of the device address are used as an opcode for the different
commands and actions that the device can perform.
Since multiple slave devices can reside on the bus, each slave device must have its own unique address
so that the master can access each device independently. After the 4-bit opcode, the following three bits
of the device address byte are comprised of the slave address bits. The three slave address bits are
preprogrammed prior to shipment and are read-only. Obtaining devices with different slave address bit
values is done by purchasing a specific ordering code. Refer to Packaging Information for explanation of
which ordering code corresponds with a specific slave address value.
Following the three slave address bits is a Read/Write select bit where a logic ‘1’ indicates a read and a
logic ‘0’ indicates a write. Upon the successful comparison of the device address, the EEPROM will return
an ACK (logic ‘0’). If the 4-bit opcode is invalid or the three bits of slave address do not match what is
preprogrammed in the device, the device will not respond on the SI/O line and will return to a Standby
state.
Table 4-1. Device Address Byte
4-bit Opcode Preprogrammed Slave Address Bits Read/Write
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Refer to Available Opcodes A2 A1 A0 R/W
Following the device address byte, a memory address byte must be transmitted to the device
immediately. The memory address byte contains a 7-bit memory array address to specify which location
in the EEPROM to start reading or writing. Refer to Table 4-2 to review these bit positions.
Table 4-2. Memory Address Byte
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Don’t Care A6 A5 A4 A3 A2 A1 A0
4.1 Memory Organization
The AT21CS01/11 internal memory array is partitioned into two regions. The main 1-Kbit EEPROM is
organized as 16 pages of eight bytes each. The Security register is 256 bits in length, organized as four
pages of eight bytes each. The lower two pages of the Security register are read-only and have a
factory‑programmed, 64‑bit serial number that is unique across all AT21CS series Serial EEPROMs. The
upper two pages of the Security register are user-programmable and can be subsequently locked (see
Locking the Security Register).
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 18
Figure 4-1. Memory Architecture Diagram
Main
1-Kbit
EEPROM
256-bit
Security
Register
Zone 2
1-Kbit Address Range (00h-7Fh)
User-Programmable Memory
Address Range (10h-1Fh)
64-bit Serial Number
Address Range (00h-07h)
Permanently Lockable
by Software
Opcode
1010b (Ah)
Opcode
1011b (Bh)
Read-Only
Four, 256-bit
ROM Zones
Each can be
independently
set to read-only
Zone 0
Zone 1
Zone 2
Zone 3
Reserved for Future Use
Address Range (08h-0Fh)
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 19
5. Available Opcodes
Table 5-1 outlines available opcodes for the AT21CS01/11.
Table 5-1. Opcodes used by the AT21CS01/11
Command 4-Bit Opcode Brief Description of Functionality
EEPROM Access 1010 (Ah) Read/Write the contents of the main memory array.
Security Register Access 1011 (Bh) Read/Write the contents of the Security register.
Lock Security Register 0010 (2h) Permanently lock the contents of the Security register.
ROM Zone Register
Access
0111 (7h) Inhibit further modification to a zone of the EEPROM array.
Freeze ROM Zone State 0001 (1h) Permanently lock the current state of the ROM Zone
registers.
Manufacturer ID Read 1100 (Ch) Query manufacturer and density of device.
Standard Speed Mode 1101 (Dh) Switch to Standard Speed mode operation (AT21CS01
only command, the AT21CS11 will NACK this command).
High-Speed Mode 1110 (Eh) Switch to High-Speed mode operation (AT21CS01/11
power‑on default. AT21CS11 will ACK this command).
5.1 EEPROM Access (Opcode Ah)
The opcode Ah is used to read data from and write data to the EEPROM. Refer to Read Operations for
more details about reading data from the device. For details about writing to the EEPROM, refer to Write
Operations.
5.2 Security Register Access (Opcode Bh)
The opcode Bh is used to read data from and write data to the Security register. Refer to Read
Operations in the Security Register for more details about reading data from the Security register. For
details about writing to the user-programmable portion of the Security register, refer to section Writing to
the Security Register.
5.3 Lock Security Register (Opcode 2h)
The opcode 2h is used to permanently lock the user-programmable portion of the Security register. Refer
to Locking the Security Register.
5.4 ROM Zone Register Access (Opcode 7h)
The AT21CS01/11 is partitioned into four, 256-bit zones, each of which can be independently and
permanently made read-only (ROM). The state of each zone is stored in a Configuration register which
can be read from or written to using the opcode 7h. The ROM Zone functionality is explained in greater
detail in ROM Zones.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 20
5.5 Freeze ROM Zone State (Opcode 1h)
The opcode 1h is used to permanently freeze the current state of the ROM Zone registers. Once set, the
ROM Zone registers are read-only.
Therefore, any zone that is not already read-only cannot be subsequently converted to ROM. Refer to
Freeze ROM Zone Registers for additional details.
5.6 Manufacturer ID Read (Opcode Ch)
Manufacturer identification, device density, and device revision information can be read from the device
using the opcode Ch. The full details of the format of the data returned by this command are found in
Manufacturer ID Read.
5.7 Standard Speed Mode (Opcode Dh)
The AT21CS01 can be set to Standard Speed mode or checked to see whether or not it is in Standard
Speed mode with the use of the Dh opcode. Further details are covered in Standard Speed Mode
(AT21CS01). The AT21CS11 does not offer Standard Speed mode and therefore will NACK this
command.
5.8 High-Speed Mode (Opcode Eh)
The AT21CS01 can be set to High-Speed mode or checked to see whether or not it is in High-Speed
mode with the use of the Eh opcode. The AT21CS11 only operates in High-Speed mode and therefore
will ACK this command. Further details are covered in High-Speed Mode.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 21
6. Write Operations
All write operations for the AT21CS01/11 begin with the master sending a Start condition, followed by a
device address byte (opcode Ah for the EEPROM and opcode Bh for the Security register) with the R/W
bit set to ‘0’ followed by the memory address byte. Next, the data value(s) to be written to the device are
sent. Data values must be sent in 8-bit increments to the device followed by a Stop condition. If a Stop
condition is sent somewhere other than at the byte boundary, the current write operation will be aborted.
The AT21CS01/11 allows single byte writes, partial page writes, and full page writes.
6.1 Device Behavior During Internal Write Cycle
To ensure that the address and data sent to the device for writing are not corrupted while any type of
internal write operation is in progress, commands sent to the device are blocked from being recognized
until the internal operation is completed. If a write interruption occurs (SI/O pulsed low) and is small
enough to not deplete the internal power storage, the device will NACK signaling that the operation is in
progress. If an interruption is longer than tDSCHG then internal write operation will be terminated and may
result in data corruption.
6.2 Byte Write
The AT21CS01/11 supports writing of a single 8-bit byte and requires a 7-bit memory word address to
select which byte to write.
Upon receipt of the proper device address byte (with opcode of Ah) and memory address byte, the
EEPROM will send a logic ‘0’ to signify an ACK. The device will then be ready to receive the data byte.
Following receipt of the complete 8-bit data byte, the EEPROM will respond with an ACK. A Stop
condition must then occur; however, since a Stop condition is defined as a null bit frame with SI/O pulled
high, the master does not need to drive the SI/O line to accomplish this. If a Stop condition is sent at any
other time, the write operation is aborted. After the Stop condition is complete, the EEPROM will enter an
internally self-timed write cycle, which will complete within a time of tWR, while the data is being
programmed into the nonvolatile EEPROM. The SI/O pin must be pulled high via the external pull-up
resistor during the entire tWR cycle. After the maximum tWR time has elapsed, the master may begin a
new bus transaction.
Note:
1. Any attempt to interrupt the internal write cycle by driving the SI/O line low may cause the byte
being programmed to be corrupted. Other memory locations within the memory array will not be
affected. Note Device Behavior During Internal Write Cycle for the behavior of the device while the
write cycle is in progress. If the master must interrupt a write operation, the SI/O line must be driven
low for tDSCHG as noted in Interrupting the Device during an Active Operation.
Figure 6-1. Byte Write
SI/O
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 0
Device Address
MSB
x A6 A5 A4 A3 A2 A1 A0
Memory Address
MSB
DDDDDDDD
Data In Byte
ACK
by Slave
`ACK
by Slave
Stop Condition
by Master
Start Condition
by Master
0 0 0
Note:
1. x = Don’t Care bit in the place of A7 as this bit falls outside the 1-Kbit addressable range.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 22
6.3 Page Write
A page write operation allows up to eight bytes to be written in the same write cycle, provided all bytes
are in the same row (address bits A6 through A3 are the same) of the memory array. Partial page writes
of less than eight bytes are allowed.
A page write is initiated the same way as a byte write, but the bus master does not send a Stop condition
after the first data byte is clocked in. Instead, after the EEPROM acknowledges receipt of the first data
byte, the bus master can transmit up to an additional seven data bytes.
The EEPROM will respond with an ACK after each data byte is received. Once all data bytes have been
sent, the device requires a Stop condition to begin the write cycle. However, since a Stop condition is
defined as a null bit frame with SI/O pulled high, the master does not need to drive the SI/O line to
accomplish this. If a Stop condition is sent at any other time, the write operation is aborted. After the Stop
condition is complete, the internally self-timed write cycle will begin.The SI/O pin must be pulled high via
the external pull-up resistor during the entire tWR cycle. Thus, in a multi‑slave environment,
communication to other single-wire devices on the bus should not be attempted while any devices are in
an internal write cycle.
The lower three bits of the memory address are internally incremented following the receipt of each data
byte. The higher order address bits are not incremented, and the device retains the memory page
location. Page write operations are limited to writing bytes within a single physical page, regardless of the
number of bytes actually being written. When the incremented word address reaches the page boundary,
the address counter will “roll over” to the beginning of the same page. Nevertheless, creating a roll over
event should be avoided as previously loaded data in the page could become unintentionally altered.
After the maximum tWR time has elapsed, the master may begin a new bus transaction.
Note:
1. Any attempt to interrupt the internal write cycle by driving the SI/O line low may cause the bytes
being programmed to be corrupted. Other memory locations within the memory array will not be
affected. Note Device Behavior During Internal Write Cycle for the behavior of the device while the
write cycle is in progress. If the master must interrupt a write operation, the SI/O line must be driven
low for tDSCHG as noted in Interrupting the Device during an Active Operation.
Figure 6-2. Page Write
SI/O
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 0
Device Address
MSB
x A6 A5 A4 A3 A2 A1 A0
Memory Address
MSB
DDDDDDDD
Data In Byte (1)
DDDDDDDD
Data In Byte (8)
ACK
by Slave
ACK
by Slave
ACK
by Slave
Stop Condition
by Master
Start Condition
by Master
00
00
Note:
1. x = Don’t Care bit in the place of A7 as this bit falls outside the 1-Kbit addressable range.
6.4 Writing to the Security Register
The Security register supports bytes writes, page writes, and partial page writes in the upper 16 bytes
(upper two pages of eight bytes each) of the region. Page writes and partial page writes in the Security
register have the same page boundary restrictions and behavior requirements as they do in the
EEPROM.
Upon receipt of the proper device address byte (with opcode of Bh specified) and memory address byte,
the EEPROM will send a logic ‘0’ to signify an ACK. The device will then be ready to receive the first data
byte.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 23
Following receipt of the data byte, the EEPROM will respond with an ACK and the master can send up to
an additional seven bytes if desired. The EEPROM will respond with an ACK after each data byte is
successfully received. Once all of the data bytes have been sent, the device requires a Stop condition to
begin the write cycle. However, since a Stop condition is defined as a null bit frame with SI/O pulled high,
the master does not need to drive the SI/O line to accomplish this. After the Stop condition is complete,
the EEPROM will enter an internally self-timed write cycle, which will complete within a time of tWR, while
the data is being programmed into the nonvolatile EEPROM. The SI/O pin must be pulled high via the
external pull-up resistor during the entire tWR cycle. Figure 6-3 is included below as an example of a byte
write operation in the Security register.
Figure 6-3. Byte Write in the Security Register
SI/O
MSB
ACK
by Slave
1 0 1 1 A2 A1 A0 0
Device Address
MSB
x x x 1 A3 A2 A1 A0
MSB
DDDDDDDD
Data In Byte
ACK
by Slave
ACK
by Slave
Stop Condition
by Master
Start Condition
by Master
0 0 0
Security Register Address
Note:
1. x = Don’t Care values in the place of A7‑A5 as these bits falls outside the addressable range of the
Security register.
2. Any attempt to interrupt the internal write cycle by driving the SI/O line low may cause the byte
being programmed to be corrupted. Other memory locations within the memory array will not be
affected. Note Device Behavior During Internal Write Cycle for the behavior of the device while the
write cycle is in progress. If the master must interrupt a write operation, the SI/O line must be driven
low for tDSCHG as noted in Interrupting the Device during an Active Operation.
6.5 Locking the Security Register
The Lock command is an irreversible sequence that will permanently prevent all future writing to the
upper 16 bytes of the Security register on the AT21CS01/11. Once the Lock command has been
executed, the entire 32-byte Security register becomes read-only. Once the Security register has been
locked, it is not possible to unlock it.
The Lock command protocol emulates a byte write operation to the Security register, however, the
opcode 0010b (2h) is required along with the A7 through A4 bits of the memory address being set to
0110b (6h). The remaining bits of the memory address, as well as the data byte are "don’t care" bits.
Even though these bits are "don’t cares", they still must be transmitted to the device. An ACK response to
the memory address and data byte indicates the Security register is not currently locked. A NACK
response indicates the Security register is already locked. Refer to Figure 6-5 for details about
determining the Lock status of the Security register.
The sequence completes with a Stop condition to initiate a self-timed internal write cycle. If a Stop
condition is sent at any other time, the Lock operation is aborted. Since a Stop condition is defined as a
null bit frame with SI/O pulled high, the master does not need to drive the SI/O line to accomplish this.
Upon completion of the write cycle, (taking a time of tWR), the Lock operation is complete and the Security
register will become permanently read-only.
Note:
1. Any attempt to drive the SI/O line low during the tWR time period may cause the Lock operation to
not complete successfully, and must be avoided.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 24
Figure 6-4. Lock Command
SI/O
MSB
ACK
by Slave
0 0 1 0 A2 A1 A0 0
Device Address
MSB
0 1 1 0 X X X X
Lock Security Register Address
MSB
XXXXXXXX
Data In Byte
ACK
by Slave
ACK
by Slave
Stop Condition
by Master
Start Condition
by Master
0 0 0
6.5.1 Device Response to a Write Command on a Locked Device
A locked device will respond differently to a Write command to the Security register compared to a device
that has not been locked. Writing to the Security register is accomplished by sending a Start condition
followed by a device address byte with the opcode of 1011b (Bh), the appropriate slave address
combination, and the Read/Write bit set as a logic ‘0’. Both a locked device and a device that has not
been locked will return an ACK. Next, the 8-bit word address is sent and again, both devices will return an
ACK. However, upon sending the data input byte, a device that has already been locked will return a
NACK and be immediately ready to accept a new command, whereas a device that has not been locked
will return an ACK to the data input byte as per normal operation for a Write command as described in
Write Operations.
6.5.2 Check Lock Command
The Check Lock command follows the same sequence as the Lock command (including 0110b in the A7
through A4 bits of the memory address byte) with the exception that only the device address byte and
memory address byte need to be transmitted to the device. An ACK response to the memory address
byte indicates that the lock has not been set while a NACK response indicates that the lock has been set.
If the lock has already been enabled, it cannot be reversed. The Check Lock command is completed by
the master sending a Stop bit to the device (defined as a null bit frame).
Figure 6-5. Check Lock Command
SI/O
MSB
ACK
by Slave
0 0 1 0 A2 A1 A0 0
Device Address
MSB
0 1 1 0 X X X X
Lock Security Register Address
ACK by Slave
if Unlocked
NACK by Slave
if Locked
Stop Condition
by Master
Start Condition
by Master
0
6.6 Setting the Device Speed
The AT21CS01 can be set to Standard Speed mode (15.4 kbps maximum) or High-Speed mode
(125 kbps maximum) through a software sequence. Upon executing a Reset and Discovery Response
sequence (see Device Reset/Power-up and Discovery Response), the device will default to High-Speed
mode. The AT21CS11 does not have Standard Speed mode.
6.6.1 Standard Speed Mode (AT21CS01)
The AT21CS01 can be set to Standard Speed mode or checked to see whether or not it is in Standard
Speed mode with the use of the Dh opcode. This transaction only requires eight bits.
To set the device to Standard Speed mode, the master must send a Start condition, followed by the
device address byte with the opcode of 1101b (Dh) specified, along with the appropriate slave address
combination and the Read/Write bit set to a logic ‘0’. The device will return an ACK (logic ‘0’) and will be
immediately ready to receive commands for standard speed operation.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 25
To determine if the device is already set to Standard Speed mode, the device address byte with the
opcode of 1101b (Dh) must be sent to the device, along with the appropriate slave address combination
and the Read/Write bit set to a logic ‘1’. The device will return an ACK (logic ‘0’) if it was set for Standard
Speed mode. It will return a NACK (logic ‘1’) if the device was not currently set for Standard Speed mode.
Note: The AT21CS11 will NACK this command.
6.6.2 High-Speed Mode
The device can be set to High-Speed mode or checked to see whether or not it is in High-Speed mode
with the use of the Eh opcode. This transaction only requires eight bits. The power-on default for the
AT21CS01/11 is High-Speed mode.
To set the device to High-Speed mode, the master must send a Start condition, followed by the device
address byte with the opcode of 1110b (Eh) specified, along the appropriate slave address combination
and the Read/Write bit set to a logic ‘0’. The device will return an ACK (Logic 0) and will be immediately
ready to receive commands for high-speed operation.
To determine if the device is already set to High-Speed mode, the device address byte with the opcode of
1110b (Eh) specified must be sent to the device along with the appropriate slave address combination
and the Read/Write bit set to a logic ‘1’. The device will return an ACK (logic ‘0’) if it was set for High-
Speed mode. It will return a NACK (logic ‘1’) if the device was not currently set for High-Speed mode.
Note: The AT21CS11 will ACK this command.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 26
7. Read Operations
Read operations are initiated in a similar way as write operations with the exception that the Read/Write
select bit in the device address byte must be set to a logic ‘1’. There are multiple read operations
supported by the device:
• Current Address Read within the EEPROM
• Random Read within the EEPROM
• Sequential Read within the EEPROM
• Read from the Security Register
• Manufacturer ID Read
Note:
1. The AT21CS01/11 contains a single, shared-memory Address Pointer that maintains the
address of the next byte in the EEPROM or Security register to be accessed. For example, if
the last byte read or written was memory location 0Dh of the EEPROM, then the Address
Pointer will be pointing to memory location 0Eh of the EEPROM. As such, when changing
from a read in one region to the other, the first read operation in the new region should begin
with a random read instead of a current address read to ensure the Address Pointer is set to
a known value within the desired region.
If the end of the EEPROM or the Security register is reached, then the Address Pointer will “roll over”
back to the beginning (address 00h) of that region. The Address Pointer retains its value between
operations as long as the pull-up voltage on the SI/O pin is maintained or as long as the device has not
been reset.
7.1 Current Address Read within the EEPROM
The internal Address Pointer must be pointing to a memory location within the EEPROM in order to
perform a current address read from the EEPROM. To initiate the operation, the master must send a Start
condition, followed by the device address byte with the opcode of 1010b (Ah) specified, along with the
appropriate slave address combination and the Read/Write bit set to a logic ‘1’. After the device address
byte has been sent, the AT21CS01/11 will return an ACK (logic ‘0’).
Following the ACK, the device is ready to output one byte (eight bits) of data. The master initiates the all
bits of data by driving the SI/O line low to start. The AT21CS01/11 will hold the line low after the master
releases it to indicate a logic ‘0’. If the data is logic ‘1’, the AT21CS01/11 will not hold the SI/O line low at
all, causing it to be pulled high by the pull-up resistor once the master releases it. This sequence repeats
for eight bits.
After the master has read the first data byte and no further data is desired, the master must return a
NACK (logic ‘1’) response to end the read operation and return the device to the Standby mode. Figure
7-1 depicts this sequence.
If the master would like the subsequent byte, it would return an ACK (logic ‘0’) and the device will be
ready output the next byte in the memory array. Refer to Sequential Read within the EEPROM for details
about continuing to read beyond one byte.
Note:
1. If the last operation to the device was an access to the Security register, then a random read should
be performed to ensure that the Address Pointer is set to a known memory location within the
EEPROM.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 27
Figure 7-1. Current Address Read
SI/O
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 1
Device Address
MSB
DDDDDDDD
Data Out Byte (n)
NACK
by Master
Stop Condition
by Master
Start Condition
by Master
0 1
7.2 Random Read within the EEPROM
A random read begins in the same way as a byte write operation which will load a new EEPROM memory
address into the Address Pointer. However, instead of sending the data byte and Stop condition of the
byte write, a repeated Start condition is sent to the device. This sequence is referred to as a “dummy
write”. After the device address and memory address bytes of the “dummy write” have been sent, the
AT21CS01/11 will return an ACK response. The master can then initiate a current address read,
beginning with a new Start condition, to read data from the EEPROM. Refer to Current Address Read
within the EEPROM for details on how to perform a current address read.
Figure 7-2. Random Read
SI/O
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 0
Device Address
Dummy Write
MSB
x A6 A5 A4 A3 A2 A1 A0
Memory Address
MSB
DDDDDDDD
Data Out Byte (n)
ACK
by Slave
NACK
by Master
Stop Condition
by Master
Start Condition
by Master
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 1
Device Address
Restart
by Master
1
0
00
7.3 Sequential Read within the EEPROM
Sequential reads start as either a current address read or as a random read. However, instead of the
master sending a NACK (logic ‘1’) response to end a read operation after a single byte of data has been
read, the master sends an ACK (logic ‘0’) to instruct the AT21CS01/11 to output another byte of data. As
long as the device receives an ACK from the master after each byte of data has been output, it will
continue to increment the address counter and output the next byte data from the EEPROM. If the end of
the EEPROM is reached, then the Address Pointer will “roll over” back to the beginning (address 00h) of
the EEPROM region. To end the sequential read operation, the master must send a NACK response after
the device has output a complete byte of data. After the device receives the NACK, it will end the read
operation and return to the Standby mode.
Note:
1. If the last operation to the device accessed the Security register, then a random read should be
performed to ensure that the Address Pointer is set to a known memory location within the
EEPROM.
Figure 7-3. Sequential Read from a Current Address Read
SI/O
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 1
Device Address
MSB
DDDDDDDD
Data Out Byte (n)
ACK
by Master
MSB
DDDDDDDD
Data Out Byte (n+x)
NACK
by Master
Stop Conditon
by Master
Start Condition
by Master
0 0 1
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 28
Figure 7-4. Sequential Read from a Random Read
SI/O
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 0
Device Address
MSB
x A6 A5 A4 A3 A2 A1 A0
Memory Address
MSB
DDDDDDDD
Data Out Byte (n)
ACK
by Slave
ACK
by Master
Stop Condition
by Master
Start Condition
by Master
MSB
ACK
by Slave
1 0 1 0 A2 A1 A0 1
Device Address
Restart
by Master
MSB
DDDDDDDD
Data Out Byte (n + x)
Dummy Write
NACK
by Master
0 10
00
7.4 Read Operations in the Security Register
The Security register can be read by using either a random read or a sequential read operation. Due to
the fact that the EEPROM and Security register share a single Address Pointer register, a “dummy write”
must be performed to correctly set the Address Pointer in the Security register. This is why a random read
or sequential read must be used as these sequences include a “dummy write.” Bits A7 through A5 are
"don’t care" bits as these fall outside the addressable range of the Security register. Current address
reads of the Security register are not supported.
In order to read the Security register, the device address byte must be specified with the opcode 1011b
(Bh) instead of the opcode 1010b (Ah).The Security register can be read to read the 64-bit serial number
or the remaining user-programmable data.
7.4.1 Serial Number Read
The lower eight bytes of the Security register contain a factory-programmed, unique, 64‑bit serial number.
In order to ensure a unique value, the entire 64-bit serial number must be read starting at Security
register address location 00h. Therefore, it is recommended that a sequential read started with a random
read operation be used, ensuring that the random read sequence uses a device address byte with
opcode 1011b (Bh) specified in addition to the memory address byte being set to 00h.
The first byte read out of the 64-bit serial number is the product identifier (A0h). Following the product
identifier, a 48-bit unique number is contained in bytes 1 through 6. The last byte of the serial number
contains a cyclic redundancy check (CRC) of the other 56 bits. The CRC is generated using the
polynomial X8 + X5 + X4 + 1. The structure of the 64-bit serial number is depicted in Table 7-1.
Table 7-1. 64-Bit Factory-Programmed Serial Number Organization
Byte 0 Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7
8-bit
Product
Identifier
(A0h)
48-bit Unique Number 8-bit CRC
Value
After all eight bytes of the serial number have been read, the master can return a NACK (logic ‘1’)
response to end the read operation and return the device to the Standby mode. If the master sends an
ACK (logic ‘0’) instead of a NACK, then the next byte (address location 08h) in the Security register will
be output. If the end of the Security register is reached, then the Address Pointer will “roll over” back to
the beginning (address location 00h) of the Security register.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 29
Figure 7-5. Serial Number Read
SI/O
MSB
ACK
by Slave
1 0 1 1 A2 A1 A0 0
Device Address
MSB
X X X 0 0 0 0 0
Serial Number Starting Address
MSB
DDDDDDDD
Serial Number Byte 00h
ACK
by Slave
ACK
by Master
Stop Condition
by Master
Start Condition
by Master
MSB
ACK
by Slave
1 0 1 1 A2 A1 A0 1
Device Address
Restart
by Master
MSB
DDDDDDDD
Serial Number Byte 07h
Dummy Write
NACK
by Master
0 1
0
00
7.5 Manufacturer ID Read
The AT21CS01/11 offers the ability to query the device for manufacturer, density, and revision
information. By using a specific opcode and following the format of a current address read, the device will
return a 24-bit value that corresponds with the I2C identifier value reserved for Microchip, along with
further data to signify a 1-Kbit density and the device revision.
To read the Manufacturer ID data, the master must send a Start condition, followed by the device address
byte with the opcode of 1100b (Ch) specified, along the appropriate slave address combination and the
Read/Write bit set to a logic ‘1’. After the device address byte has been sent, the AT21CS01/11 will return
an ACK (logic ‘0’). If the Read/Write bit is set to a logic ‘0’ to indicate a write, the device will NACK (logic
‘1’) since the Manufacturer ID data is read-only.
After the device has returned an ACK, it will then send the first byte of Manufacturer ID data which
contains the eight Most Significant bits (D23‑D16) of the 24-bit data value. The master can then return an
ACK (logic ‘0’) to indicate it successfully received the data, upon which the device will send the second
byte (D15‑D8) of Manufacturer ID data. The process repeats until all three bytes have been read out and
the master sends a NACK (logic ‘1’) to complete the sequence. Figure 7-6 depicts this sequence below. If
the master ACKs (logic ‘0’) the third byte, the Internal Pointer will roll over back to the first byte of
Manufacturer ID data.
Figure 7-6. Manufacturer ID Read
SI/O
MSB
ACK
by Slave
1 1 0 0 A2 A1 A0 1
Device Address
MSB
(D23)
DDDDDDDD
Manufacturer ID Byte 1
ACK
by Master
DDDDDDDD
Manufacturer ID Byte 2
NACK
by Master
Stop Condition
by Master
Start Condition
by Master
ACK
by Master
LSB
(D0)
DDDDDDDD
Manufacturer ID Byte 3
0 100
Table 7-2 below provides the format of the Manufacturer ID data.
Table 7-2. Manufacturer ID Data Format
Device Manufacturer Code
<D23:D12>
Device Code
<D11:D3>
Revision Code
<D2:D0>
Hex Value
<D23:D0>
AT21CS01 0000-0000-1101 0010-0000-0 000 00D200h
AT21CS11 0000-0000-1101 0011-1000-0 000 00D380h
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 30
The Manufacturer Identifier portion of the ID is returned in the 12 Most Significant bits of the three bytes
read out. The value reserved for Microchip is 0000-0000-1101b (00Dh). Therefore, the first byte read
out by the device will be 00h. The upper nibble of the second byte read out is Dh.
The Least Significant 12 bits of the 24-bit ID is comprised of a Microchip defined value that indicates the
device density and revision. Bits D11 through D3 indicate the device code and bits D2 through D0
indicate the device revision. The output is shown more specifically in Table 7-2.
The overall 24-bit value returned by the AT21CS01 is 00D200h. The overall 24‑bit value returned by the
AT21CS11 is 00D380h.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 31
8. ROM Zones
8.1 ROM Zone Size and ROM Zone Registers
Certain applications require that portions of the EEPROM memory array be permanently protected
against malicious attempts at altering program code, data modules, security information, or
encryption/decryption algorithms, keys, and routines. To address these applications, the memory array is
segmented into four different memory zones of 256 bits each. A ROM Zone mechanism has been
incorporated that allows any combination of individual memory zones to be permanently locked so that
they become read‑only (ROM). Once a memory zone has been converted to ROM, it can never be
erased or programmed again, and it can never be unlocked from the ROM state. Table 8-2 shows the
address range of each of the four memory zones.
8.1.1 ROM Zone Registers
Each 256-bit memory zone has a corresponding single-bit ROM Zone register that is used to control the
ROM status of that zone. These registers are nonvolatile and will retain their state even after a device
power cycle or Reset operation. The following table outlines the two states of the ROM Zone registers.
Each ROM Zone register has specific ROM Zone register address that is reserved for read or write
access.
Table 8-1. ROM Zone Register Values
Value ROM Zone Status
0 ROM Zone is not enabled and that memory zone can be programmed and erased (the default
state).
1 ROM Zone is enabled and that memory zone can never be programmed or erased again.
Issuing the ROM Zone command to a particular ROM Zone register address will set the corresponding
ROM Zone register to the logic ‘1’ state. Each ROM Zone register can only be set once; therefore, once
set to the logic ‘1’ state, a ROM Zone cannot be reset back to the logic ‘0’ state.
Table 8-2. ROM Zone Address Ranges
Memory Zone Starting Memory Address Ending Memory Address ROM Zone
Register Address
0 0h 1Fh 01h
1 20h 3Fh 02h
2 40h 5Fh 04h
3 60h 7Fh 08h
8.2 Programming and Reading the ROM Zone Registers
8.2.1 Reading the Status of a ROM Zone Register
To check the current status of a ROM Zone register, the master must emulate a random read sequence
with the exception that the opcode 0111b (7h) will be used. The dummy write portion of the random read
sequence is needed to specify which ROM Zone register address is to be read.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 32
This sequence begins by the master sending a Start condition, followed by a device address byte with the
opcode of 7h in the four Most Significant bits, along with the appropriate slave address combination and
the Read/Write bit set to a logic ‘0’. The AT21CS01/11 will respond with an ACK.
Following this device address byte is an 8-bit ROM Zone register address byte. The four Most Significant
bits are not used and are therefore "don’t care" bits. The address sent to the device must match one of
the ROM Zone register addresses specified in Table 8-3. After the ROM Zone register address has been
sent, the AT21CS01/11 will return an ACK (logic ‘0’).
Then an additional Start condition is sent to the device with the same device address byte as before, but
now with the Read/Write bit set to a logic ‘1’, to which the device will return an ACK. After the
AT21CS01/11 has sent the ACK, the device will output either 00h or FFh data byte. A 00h data byte
indicates that the ROM Zone register is zero, meaning the zone has not been set as ROM. If the device
outputs FFh data, then the memory zone has been set to ROM and cannot be altered.
Table 8-3. Read ROM Zone Register – Output Data
Output Data ROM Zone Register Value
00h ROM Zone register value is zero (zone is not set as ROM).
FFh ROM Zone register value is one (zone is permanently set as ROM).
Figure 8-1. Reading the State of a ROM Zone Register
SI/O
MSB
ACK
by Slave
0 1 1 1 A2 A1 A0 0
Device Address
Dummy Write
MSB
0 0 0 0 A3 A2 A1 A0
ROM Zone Register Address
MSB
DDDDDDDD
Data Out Byte (00h or FFh)
ACK
by Slave
NACK
by Master
Stop Condition
by Master
Start Condition
by Master
MSB
ACK
by Slave
0 1 1 1 A2 A1 A0 1
Device Address
Restart
by Master
1
0
00
8.2.2 Writing to a ROM Zone Register
A ROM Zone register can only be written to a logic ‘1’ which will set the corresponding memory zone to a
ROM state. Once a ROM Zone register has been written, it can never be altered again.
To write to a ROM Zone register, the master must send a Start condition, followed by the device address
byte with the opcode of 0111b (7h) specified, along with the appropriate slave address combination and
the Read/Write bit set to a logic ‘0’. The device will return an ACK. After the device address byte has
been sent, the AT21CS01/11 will return an ACK.
Following the device address byte is an 8-bit ROM Zone register address byte. The address sent to the
device must match one of the ROM Zone register addresses specified in Table 8-2. After the ROM Zone
register address has been sent, the AT21CS01/11 will return an ACK.
After the AT21CS01/11 has sent the ACK, the master must send an FFh data byte in order to set the
appropriate ROM Zone register to the logic ‘1’ state. The device will then return an ACK and, after a Stop
condition is executed, the device will enter a self-time internal write cycle, lasting tWR. If a Stop condition
is sent at any other point in the sequence, the write operation to the ROM Zone register is aborted. The
device will not respond till any commands until the tWR time has completed. This sequence is depicted in
Figure 8-2.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 33
Figure 8-2. Writing to a ROM Zone Register
SI/O
MSB
ACK
by Slave
0 1 1 1 A2 A1 A0 0
Device Address
MSB
0 0 0 0 A3 A2 A1 A0
ROM Zone Register Address
MSB
11111111
Data In Byte (FFh)
ACK
by Slave
ACK
by Slave
Stop Condition
by Master
Start Condition
by Master
0 0 0
Note:
1. Any attempt to interrupt the internal write cycle by driving the SI/O line low may cause the register
being programmed to become corrupted. Note Device Behavior During Internal Write Cycle for the
behavior of the device while a write cycle is in progress. If the master must interrupt a write
operation, the SI/O line must be driven low for tDSCHG as noted in Interrupting the Device during an
Active Operation.
8.2.3 Freeze ROM Zone Registers
The current ROM Zone state can be frozen so that no further modifications to the ROM Zone registers
can be made. Once frozen, this event cannot be reversed.
To freeze the state of the ROM Zone registers, the master must send a Start condition, followed by the
device address byte with the opcode of 0001b (1h) specified, along with the appropriate slave address
combination and the Read/Write bit set to a logic ‘0’. The device will return either an ACK (logic ‘0’)
response if the ROM Zone registers have not been previously frozen or a NACK (logic ‘1’) response if the
registers have already been frozen.
If the AT21CS01/11 returns an ACK, the master must send a fixed arbitrary address byte value of 55h, to
which the device will return an ACK (logic ‘0’). Following the 55h address byte, a data byte of AAh must
be sent by the master. The device will ACK after the AAh data byte. If an address byte other than 55h or
a data byte other than AAh is sent, the device will NACK (logic ‘1’) and the freeze operation will not be
performed.
To complete the Freeze ROM Zone register sequence, a Stop condition is required. If a Stop condition is
sent at any other point in this sequence, the operation is aborted. Since a Stop condition is defined as a
null bit frame with SI/O pulled high, the master does not need to drive the SI/O line to accomplish this.
After the Stop condition is complete, the internally self-timed write cycle will begin.The SI/O pin must be
pulled high via the external pull-up resistor during the entire tWR cycle.
Figure 8-3. Freezing the ROM Zone Registers
SI/O
MSB
ACK
by Slave
0 0 0 1 A2 A1 A0 0
Device Address
MSB
01010101
Fixed Abitrary Address (55h)
MSB
10101010
Data In Byte (AAh)
ACK
by Slave
ACK
by Slave
Stop Condition
by Master
Start Condition
by Master
0 0 0
Note:
1. Any attempt to drive the SI/O line low during the tWR time period may cause the Freeze operation to
not complete successfully, and must be avoided.
8.3 Device Response to a Write Command Within an Enabled ROM Zone
The AT21CS01/11 will respond differently to a Write command in a memory zone that has been set to
ROM compared to Write command in a memory zone that has not been set to ROM. Writing to the
EEPROM is accomplished by sending a Start condition followed by a device address byte with the
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 34
opcode of 1010b (Ah), the appropriate slave address combination, and the Read/Write bit set as a
logic ‘0’. Since a memory address has not been input at this point in the sequence, the device returns an
ACK. Next, the 8‑bit word address is sent which will result in an ACK from the device, regardless if that
address is in a memory zone that has been set to ROM. However, upon sending the data input byte, a
Write command to an address that was in a memory zone that was set to ROM will result in a NACK
response from the AT21CS01/11 and the device will be immediately ready to accept a new command. If
the address being written was in a memory zone that had not been set to ROM, the device will return an
ACK to the data input byte as per normal operation for write operations as described in Write Operations.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 35
9. Device Default Condition from Microchip
The AT21CS01/11 is delivered with the EEPROM array set to logic ‘1’ state resulting in FFh data in all
locations.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 36
10. Packaging Information
10.1 Package Marking Information
DRAWING NO. REV. TITLE
21CS01/11SM A
9/11/17
AT21CS01/11SM,AT21CS01 and AT21CS11 Package
Marking Information
YYWWNNN
### % CO
ATMLHYWW
8-lead SOIC
Note 2: Package drawings are not to scale
Note 1: designates pin 1
AT21CS01/AT21CS11: Package Marking Information
Diagram Order: EIAJ, PDIP, SOIC,TSSOP, UDFN, SOT23,VFBGA,XDFN
Catalog Number Truncation
AT21CS01
AT21CS11
Truncation Code ###: K1M
Truncation Code ###: K2
Date Codes Slave Address
Y = Year M = Month WW = Work Week of Assembly % = Slave Address
7: 2017 1: 2021 A: January 02: Week 2 A: Address 000 E: Address 100
8: 2018 2: 2022 B: February 04: Week 4 B: Address 001 F: Address 101
9: 2019 3: 2023 ... ... C: Address 010 G: Address 110
0: 2020 4: 2024 L: December 52: Week 52 D: Address 011 H: Address 111
Country of Assembly Trace Code Atmel Truncation
CO = Country of Assembly NNN or NN AT: Atmel
ATM: Atmel
ATML: Atmel
l
WWNNN
3-lead SOT-23
NN
4-ball WLCSP
ATML
###%Y
WWNNN
2-ld XSFN
(AT21CS01 only)
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 37
DRAWING NO. REV. TITLE GPC
2MS-1 B
10/14/14
2MS-1, 2-pad 5.0x3.5 mm Body, 0.40 thick,
Extra Thin Single Flat No Lead Package (XSFN) YDR
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN TYP MAX NOTE
A 0.30 0.35 0.40
A1 0.00 0.035 0.05
A3 0.127 REF
b 1.05 1.10 1.15 3
L 4.55 4.60 4.65
D 5.00 BSC
E 3.50 BSC
e 2.00 BSC
0 0° - - 2
K 0.90 REF
Notes:
1. Dimensioning and tolerancing conform to ASME Y14.5M - 1994.
2. All dimensions are in millimeters, 0 is in degrees.
3. Dimension ‘b’ applies to metallized terminal and is measured between 0.15
and 0.30mm from terminal tip. If the terminal has the optional radius on the
other end of the terminal, the dimension ‘b’ should not be measured in that
radius area.
4. Maximum package warpage is 0.05mm.
5. Maximum allowable burrs is 0.076mm in all directions.
6. Pin #1 on top will be laser marked.
7. Unilateral coplanarity zone applies to the exposed heat sink slug as well as
the terminals.
0.10
mCA B
v0.05 C3
6
TOP VIEW BOTTOM VIEW
(DATUM A)
B
A
k0.10 C
4X
Pin1 Corner
(DATUM B)
1
2
A1
SEATING PLANE
A3 C
SIDE VIEW
1
2
D
E
A
7
0
C0.60 X 45°
e
b
L
0.200
0.200
K
7
Pin1 Corner
m
k0.050 C
h0.10 C
Note: For the most current package drawings, please see the Microchip Packaging Specification located
at http://www.microchip.com/packaging.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 38
AT21CS01 [DATASHEET]
Atmel-8903A-SEEPROM-AT21CS01-Datasheet_082015
34
12.2 3ST1 — 3-lead SOT23
TITLE DRAWING NO.GPC REV.
3TS1
12/11/09
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
End View
Side View
Top View
3TS1, 3-lead, 1.30mm Body, Plastic Thin
Shrink Small Outline Package (Shrink SOT)
BTBG
0.89
0.01
0.88
2.80
2.10
1.20
0.30
A
A1
A2
D
E
E1
L1
e1
b
-
-
-
2.90
-
1.30
0.54 REF
1.90 BSC
-
1.12
0.10
1.02
3.04
2.64
1.40
0.50
1,2
1,2
3
Notes: 1. Dimension D does not include mold flash, protrusions or gate
burrs. Mold flash, protrusions or gate burrs shall not exceed
0.25mm per end. Dimension E1 does not include interlead flash
or protrusion. Interlead flash or protrusion shall not exceed
0.25mm per side.
2. The package top may be smaller than the package bottom.
Dimensions D and E1 are determined at the outermost extremes
of the plastic body exclusive of mold flash, tie bar burrs, gate
burrs and interlead flash, but including any mismatch between
the top and bottom of the plastic body.
3. These dimensions apply to the flat section of the lead between
0.08 mm and 0.15mm from the lead tip.
This drawing is for general information only. Refer to JEDEC
Drawing TO-236, Variation AB for additional information.
C
L
L1
3
E
E1
12
e1
SEATING
PLANE
b
A2 A
A1e
D
GND
SDA VCC
Note: For the most current package drawings, please see the Microchip Packaging Specification located
at http://www.microchip.com/packaging.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 39
33
AT21CS01 [DATASHEET]
Atmel-8903A-SEEPROM-AT21CS01-Datasheet_082015
12. Packaging Information
12.1 8S1 — 8-lead SOIC
DRAWING NO. REV. TITLE GPC
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
A1 0.10 – 0.25
A – – 1.75
b 0.31 – 0.51
C 0.17 – 0.25
D 4.90 BSC
E 6.00 BSC
E1 3.90 BSC
e 1.27 BSC
L 0.40 – 1.27
Ø
Ø
0° – 8°
Ø
E
1
N
TOP VIEW
C
E1
END VIEW
A
b
L
A1
e
D
SIDE VIEW
8S1 H
3/6/2015
Notes: This drawing is for general information only.
Refer to JEDEC Drawing MS-012, Variation AA
for proper dimensions, tolerances, datums, etc.
8S1, 8-lead (0.150” Wide Body), Plastic Gull Wing
Small Outline (JEDEC SOIC) SWB
Note: For the most current package drawings, please see the Microchip Packaging Specification located
at http://www.microchip.com/packaging.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 40
35
AT21CS01 [DATASHEET]
Atmel-8903A-SEEPROM-AT21CS01-Datasheet_082015
12.3 4U-6 — 4-ball WLCSP
DRAWING NO. REV. TITLE GPC
4U-6 B
8/7/15
4U-6, 4-ball 2x2 Array, 0.40mm Pitch
Wafer Level Chip-Scale Package (WLCSP) with BSC GPH
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN TYP MAX NOTE
A 0.313 0.334 0.355
A1 — 0.094 —
A2 — 0.240 — 3
D Contact Microchip for details
d1 0.400 BSC
E Contact Microchip for details
e1 0.400 BSC
b 0.170 0.185 0.200
PIN ASSIGNMENT MATRIX
1 2
A
B
SI/O
GND
NC
NC
TOP VIEW
SIDE VIEW
BOTTOM SIDE
Note: 1. Dimensions are NOT to scale.
2. Solder ball composition is 95.5Sn-4.0Ag-0.5Cu.
3. Product offered with Back Side Coating.
k0.015 (4X)
A
B
C
k0.075 C
SEATING PLANE
db
A1 CORNER
A1 CORNER
d0.015 mC
v0.05 C A B
m
d
D
E
d1
e1
A2
A1
A
A
B
12
B
A
1 2
Note: For the most current package drawings, please see the Microchip Packaging Specification located
at http://www.microchip.com/packaging.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 41
11. Revision History
Atmel AT21CS01 Document 8903 Revision A (August 2015)
Initial document release.
Atmel AT21CS11 Document 8975 Revision A (August 2015)
Initial document release, Preliminary Status.
Atmel AT21CS11 Document 8975 Revision B (November 2015)
Removed Standard Speed mode
Revision A (October 2017)
Updated to Microchip template. This replaces Atmel documents 8903 and 8975. Added XSFN package.
Updated DC output current absolute maximum rating. Removed lead finish designation. Updated trace
code format in package markings.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 42
The Microchip Web Site
Microchip provides online support via our web site at http://www.microchip.com/. This web site is used as
a means to make files and information easily available to customers. Accessible by using your favorite
Internet browser, the web site contains the following information:
•Product Support – Data sheets and errata, application notes and sample programs, design
resources, user’s guides and hardware support documents, latest software releases and archived
software
•General Technical Support – Frequently Asked Questions (FAQ), technical support requests,
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Subscribers will receive e-mail notification whenever there are changes, updates, revisions or errata
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To register, access the Microchip web site at http://www.microchip.com/. Under “Support”, click on
“Customer Change Notification” and follow the registration instructions.
Customer Support
Users of Microchip products can receive assistance through several channels:
• Distributor or Representative
• Local Sales Office
• Field Application Engineer (FAE)
• Technical Support
Customers should contact their distributor, representative or Field Application Engineer (FAE) for support.
Local sales offices are also available to help customers. A listing of sales offices and locations is included
in the back of this document.
Technical support is available through the web site at: http://www.microchip.com/support
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 43
Product Identification System
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
Tape and Reel
Option
PART NO. XX X X
Device Package Device
Grade
Operating
Voltage
Product
Variation
XX X[1]
Device: AT21CS01/11: Single-Wire, I/O Powered 1‑Kbit (128 x 8) Serial EEPROM
with Unique, Factory‑Programmed 64‑bit Serial Number
Package Option: MS = 2-Pad XSFN
ST = 3-Lead SOT23
SS = 8-Lead SOIC
U= 4-Ball WLCSP (AT21CS01 only)
WWU = Wafer Unsawn
Package Device Grade or
Wafer/Die Thickness: H= Green, Industrial Temperature Range (-40°C to +85°C)
U= Green, Industrial Temperature Range (‑40°C to +85°C)
11 = 11 mil Wafer Thickness
Operating Voltage: M= 1.7V to 3.6V (AT21CS01)
blank = 2.7V to 4.5V (AT21CS11)
Product Variation: 10 = 0-0-0 Slave Address (A2, A1, A0)(2)
0B = 0-0-0 Slave Address (A2, A1, A0), WLCSP package with Back
Side Coating
Tape and Reel Option: B= Standard packaging (tube or tray)
T= Tape and Reel(1)
Note:
1. Tape and Reel identifier only appears in the catalog part number description. This identifier is used
for ordering purposes and is not printed on the device package. Check with your Microchip Sales
Office for package availability with the Tape and Reel option.
2. Please contact Microchip Sales to order devices with non 0-0-0 slave addresses.
Examples:
• AT21CS01-SSHM10-T, 1.7V-3.6V, Industrial Temp., Tape and Reel, SOIC package,
Slave Address 0-0-0
• AT21CS01-SSHM11-B, 1.7V-3.6V, Industrial Temp., SOIC package, Slave Address 0-0-1(2)
• AT21CS01-MSHM15-T, 1.7V-3.6V, Industrial Temp., Tape and Reel, XSFN package,
Slave Address 1-0-1(2)
• AT21CS01-UUM0B-T, 1.7V-3.6V, Industrial Temp., Tape and Reel, UDFN package,
Slave Address 0-0-0
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 44
• AT21CS11-STU10, 2.7V-4.5V, Industrial Temp., SOT23 package, Slave Address 0-0-0
• AT21CS11-MSH17-T, 2.7V-4.5V, Industrial Temp., XSFN package, Slave Address 1-1-1(2)
• AT21CS11-WWU11(1), 2.7V-4.5V, Industrial Temp., 11 mil Thick Wafer Thickness,
Slave Address 0-0-0 all die
Note:
1. Contact Microchip Sales for wafer sales.
2. Please contact Microchip Sales to order non 0-0-0 slave addressed devices.
Microchip Devices Code Protection Feature
Note the following details of the code protection feature on Microchip devices:
• Microchip products meet the specification contained in their particular Microchip Data Sheet.
• Microchip believes that its family of products is one of the most secure families of its kind on the
market today, when used in the intended manner and under normal conditions.
• There are dishonest and possibly illegal methods used to breach the code protection feature. All of
these methods, to our knowledge, require using the Microchip products in a manner outside the
operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is
engaged in theft of intellectual property.
• Microchip is willing to work with the customer who is concerned about the integrity of their code.
• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their
code. Code protection does not mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the
code protection features of our products. Attempts to break Microchip’s code protection feature may be a
violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software
or other copyrighted work, you may have a right to sue for relief under that Act.
Legal Notice
Information contained in this publication regarding device applications and the like is provided only for
your convenience and may be superseded by updates. It is your responsibility to ensure that your
application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY
OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS
CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE.
Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life
support and/or safety applications is entirely at the buyer’s risk, and the buyer agrees to defend,
indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting
from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual
property rights unless otherwise stated.
Trademarks
The Microchip name and logo, the Microchip logo, AnyRate, AVR, AVR logo, AVR Freaks, BeaconThings,
BitCloud, CryptoMemory, CryptoRF, dsPIC, FlashFlex, flexPWR, Heldo, JukeBlox, KeeLoq, KeeLoq logo,
Kleer, LANCheck, LINK MD, maXStylus, maXTouch, MediaLB, megaAVR, MOST, MOST logo, MPLAB,
OptoLyzer, PIC, picoPower, PICSTART, PIC32 logo, Prochip Designer, QTouch, RightTouch, SAM-BA,
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 45
SpyNIC, SST, SST Logo, SuperFlash, tinyAVR, UNI/O, and XMEGA are registered trademarks of
Microchip Technology Incorporated in the U.S.A. and other countries.
ClockWorks, The Embedded Control Solutions Company, EtherSynch, Hyper Speed Control, HyperLight
Load, IntelliMOS, mTouch, Precision Edge, and Quiet-Wire are registered trademarks of Microchip
Technology Incorporated in the U.S.A.
Adjacent Key Suppression, AKS, Analog-for-the-Digital Age, Any Capacitor, AnyIn, AnyOut, BodyCom,
chipKIT, chipKIT logo, CodeGuard, CryptoAuthentication, CryptoCompanion, CryptoController,
dsPICDEM, dsPICDEM.net, Dynamic Average Matching, DAM, ECAN, EtherGREEN, In-Circuit Serial
Programming, ICSP, Inter-Chip Connectivity, JitterBlocker, KleerNet, KleerNet logo, Mindi, MiWi,
motorBench, MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, MultiTRAK, NetDetach, Omniscient
Code Generation, PICDEM, PICDEM.net, PICkit, PICtail, PureSilicon, QMatrix, RightTouch logo, REAL
ICE, Ripple Blocker, SAM-ICE, Serial Quad I/O, SMART-I.S., SQI, SuperSwitcher, SuperSwitcher II, Total
Endurance, TSHARC, USBCheck, VariSense, ViewSpan, WiperLock, Wireless DNA, and ZENA are
trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated in the U.S.A.
Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries.
GestIC is a registered trademark of Microchip Technology Germany II GmbH & Co. KG, a subsidiary of
Microchip Technology Inc., in other countries.
All other trademarks mentioned herein are property of their respective companies.
© 2017, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved.
ISBN: 978-1-5224-2232-7
Quality Management System Certified by DNV
ISO/TS 16949
Microchip received ISO/TS-16949:2009 certification for its worldwide headquarters, design and wafer
fabrication facilities in Chandler and Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures are for its PIC® MCUs and dsPIC®
DSCs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design and manufacture of development
systems is ISO 9001:2000 certified.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc. Datasheet DS20005857A-page 46
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