MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
EVALUATION KIT AVAILABLE
General Description
The MAX6955 is a compact display driver that interfaces
microprocessors to a mix of 7-segment, 14-segment,
and 16-segment LED displays through an I2C-compati-
ble 2-wire serial interface. The MAX6955 drives up to 16
digits 7-segment, 8 digits 14-segment, 8 digits 16-seg-
ment, or 128 discrete LEDs, while functioning from a
supply voltage as low as 2.7V. The driver includes five
I/O expander or general-purpose I/O (GPIO) lines, some
or all of which can be configured as a key-switch reader.
The key-switch reader automatically scans and
debounces a matrix of up to 32 switches.
Included on chip are full 14- and 16-segment ASCII
104-character fonts, a hexadecimal font for 7-segment
displays, multiplex scan circuitry, anode and cathode
drivers, and static RAM that stores each digit. The max-
imum segment current for the display digits is set using
a single external resistor. Digit intensity can be inde-
pendently adjusted using the 16-step internal digital
brightness control. The MAX6955 includes a low-power
shutdown mode, a scan-limit register that allows the
user to display from 1 to 16 digits, segment blinking
(synchronized across multiple drivers, if desired), and a
test mode, which forces all LEDs on. The LED drivers
are slew-rate limited to reduce EMI.
For an SPI-compatible version, refer to the MAX6954
data sheet. An evaluation kit (EV kit) for the MAX6955 is
available.
Applications
Set-Top Boxes Bar Graph Displays
Panel Meters Audio/Video Equipment
White Goods
Benefits and Features
•Simplifies Driving 5 x 7 Matrix LED Displays
•Drives Common-Cathode Monocolor and Bicolor
LED Displays
•Drives Up to 16 Digits 7-Segment, 8 Digits 14-Segment,
8 Digits 16-Segment, 128 Discrete LEDs, or a
Combination of Digit Types
•2.7V to 5.5V Operation
•Standard 2-Wire Interface Supports a Variety of
Microprocessor Architectures
•400kbps 2-Wire I2C-Compatible Interface
•Integrated Flexibility Supports Different Application
Requirements
•Built-In ASCII 104-Character Font for 14-Segment
and 16-Segment Digits and Hexadecimal Font for
7-Segment Digits
•16-Step Digit-by-Digit Digital Brightness Control
•Display Blanked on Power-Up
•Automatic Blinking Control for Each Segment
•10µA (typ) Low-Power Shutdown (Data Retained)
•Five GPIO Port Pins Can Be Configured as Key-Switch
Reader to Scan and Debounce Up to 32 Switches with
n-Key Rollover
•IRQ Output when a Key Input Is Debounced
•Slew-Rate-Limited Segment Drivers for Lower EMI
•36-Pin SSOP and 40-Pin DIP and TQFN Packages
•Automotive Temperature Range Standard Covers
Usage in Harsh Environments
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX6955AAX+ -40°C to +125°C 36 SSOP
MAX6955ATL+ -40°C to +125°C 40 TQFN-EP*
Pin Configurations and Typical Operating Circuits appear
at end of data sheet.
ISET
OSC
OSC_OUT
BLINK
SCL
AD0
AD1
SDA
2-WIRE SERIAL INTERFACE
RAM
BLINK
CONTROL
CONFIGURATION
REGISTER
CHARACTER
GENERATOR
ROM
CURRENT
SOURCE
DIVIDER/
COUNTER
NETWORK
DIGIT
MULTIPLEXER
PWM
BRIGHTNESS
CONTROL
GPIO
AND KEY-SCAN
CONTROL
LED
DRIVERS
O0 TO O18
P0 TO P4/IRQ
MAX6955
Functional Diagram
*
EP = Exposed pad.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
19-2548; Rev 4; 7/15
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 2www.maximintegrated.com
Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage (with Respect to GND)
V+ .........................................................................-0.3V to +6V
SCL, SDA, AD0, AD1 ...........................................-0.3V to +6V
All Other Pins............................................-0.3V to (V+ + 0.3V)
Current
O0–O7 Sink Current ......................................................935mA
O0–O18 Source Current .................................................55mA
SCL, SDA, AD0, AD1, BLINK, OSC, OSC_OUT, ISET ....20mA
P0, P1, P2, P3, P4/IRQ ....................................................40mA
GND .....................................................................................1A
Continuous Power Dissipation (TA= +70°C)
36-Pin SSOP (derate at 11.8mW/°C above +70°C) .....941mW
40-Pin TQFN (derate at 25.6mW/°C above +70°C)....2051.3mW
Operating Temperature Range
(TMIN to TMAX) ...............................................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
DC Electrical Characteristics
(Typical Operating Circuit, V+ = 2.7V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONSMIN TYP MAX UNITS
Operating Supply Voltage V+ 2.7 5.5 V
TA = +25°C 10 35
Shutdown Supply Current ISHDN
Shutdown mode, all
digital inputs at V+
or GND TA = TMIN to TMAX 40
µA
TA = +25°C 22 30
Operating Supply Current I+
All segments on, all
digits scanned,
intensity set to full,
internal oscillator, no
display or OSC_OUT
load connected
TA = TMIN to TMAX 35
mA
OSC = RC oscillator, RSET = 56kΩ,
CSET = 22pF, V+ = 3.3V 4
Master Clock Frequency fOSC
OSC driven externally 1 8
MHz
Dead Clock Protection Frequency fOSC 95 kHz
OSC Internal/External Detection
Threshold VOSC 1.7 V
OSC High Time tCH 50 ns
OSC Low Time tCL 50 ns
Slow Segment Blink Period fSLOWBLINK
OSC = RC oscillator, RSET = 56kΩ,
CSET = 22pF, V+ = 3.3V 1s
Fast Segment Blink Period fFASTBLINK OSC = RC oscillator, RSET = 56kΩ,
CSET = 22pF, V+ = 3.3V 0.5 s
Fast or Slow Segment Blink Duty
Cycle 49.5 50.5 %
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 3www.maximintegrated.com
DC Electrical Characteristics (continued)
(Typical Operating Circuit, V+ = 2.7V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONSMIN TYP MAX UNITS
VLED = 2.2V,
V+ = 3.3V
Segment Drive Source Current ISEG VLED = 2.2V,
V+ = 2.7V
TA = +25°C -32 -40 -48 mA
Segment Current Slew Rate ∆ISEG/∆tT
A = +25°C, V+ = 3.3V 11 mA/µs
Segment Drive Current Matching ∆ISEG TA = +25°C, V+ = 3.3V 5 %
LOGIC INPUTS AND OUTPUTS
Input High Voltage
SDA, SCL, AD0, AD1 VIH 0.7 x
V+ V
Input Low Voltage
SDA, SCL, AD0, AD1 VIL 0.3 x
V+ V
Input Leakage Current
SDA, SCL, AD0, AD1, OSC, P0,
P1, P2, P3, P4/IRQ
IIH, IIL -1 +1 µA
SDA Output Low Voltage VOLSDA ISINK = 6mA 0.4 V
Port Logic-High Input Voltage
P0, P1, P2, P3, P4/IRQ VIHP 0.7 x
V+ V
Port Logic-Low Input Voltage
P0, P1, P2, P3, P4/IRQ VILP 0.3 x
V+ V
Port Hysteresis Voltage
P0, P1, P2, P3, P4/IRQ ∆VIP 0.03 x
V+ V
Port Input Pullup Current from V+ IIPU P0 to P3 configured as key-scan inputs,
V+ = 3.3V 75 µA
Port Output Low Voltage VOLP ISINK = 8mA 0.3 0.5 V
Blink Output Low Voltage VOLBK ISINK = 0.6mA 0.1 0.3 V
OSC_OUT Output High Voltage VOHOSC ISOURCE = 1.6mA V+ -
0.4 V
OSC_OUT Output Low Voltage VOLOSC ISINK = 1.6mA 0.4 V
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 4www.maximintegrated.com
Timing Characteristics
(Typical Operating Circuit, V+ = 2.7V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONSMIN TYP MAX UNITS
TIMING CHARACTERISTICS
Serial Clock Frequency fSCL 400 kHz
Bus Free Time Between a STOP
and a START Condition tBUF 1.3 µs
Hold Time (Repeated) START
Condition tHD
,
tSTA 0.6 µs
Repeated START Condition Setup
Time tSU, tSTA 0.6 µs
STOP Condition Setup Time tSU:STO 0.6 µs
Data Hold Time tHD, tDAT (Note 3) 0.9 µs
Data Setup Time tSU, tDAT 100 ns
SCL Clock Low Period tLOW 1.3 µs
SCL Clock High Period tHIGH 0.6 µs
Rise Time of Both SDA and SCL
Signals, Receiving tR(Notes 2, 4) 20 +
0.1CB300 ns
Fall Time of Both SDA and SCL
Signals, Receiving tF(Notes 2, 4) 20 +
0.1CB300 ns
Fall Time of SDA Transmitting tF, tX(Notes 2, 5) 20 +
0.1CB300 ns
Pulse Width of Spike Suppressed tSP (Notes 2, 6) 0 50 ns
Capacitive Load for Each
Bus Line CB(Note 2) 400 pF
Note 1: All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design.
Note 3: A master device must provide a hold time of at least 300ns for the SDA signal (referred to VIL- of the SCL signal) in order to
bridge the undefined region of SCL’s falling edge.
Note 4: CB= total capacitance of one bus line in pF. tRand tFmeasured between 0.3V+ and 0.7V+.
Note 5: ISINK ≤6mA. CB= total capacitance of one bus line in pF. tRand tFmeasured between 0.3V+ and 0.7V+.
Note 6: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 5www.maximintegrated.com
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX6955 toc01
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (MHz)
110805020-10
3.8
4.0
4.2
4.4
3.6
-40
RSET = 56kΩ
CSET = 22pF
SUPPLY VOLTAGE (V)
5.04.54.03.53.02.5 5.5
INTERNAL OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX6955 toc02
OSCILLATOR FREQUENCY (MHz)
3.8
4.0
4.2
4.4
3.6
RSET = 56kΩ
CSET = 22pF
100ns/div
OSC: 500mV/div
OSC_OUT: 2V/div
MAX6954 toc03
OSC
0V
0V
OSC_OUT
INTERNAL OSCILLATOR WAVEFORM
AT OSC AND OSC_OUT PINS
RSET = 56kΩ
CSET = 22pF
DEAD CLOCK OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
85
90
95
100
105
110
80
SUPPLY VOLTAGE (V)
5.04.54.03.53.02.5 5.5
MAX6955 toc04
OSCILLATOR FREQUENCY (MHz)
RSET = 56kΩ
CSET = GND
CURRENT NORMALIZED TO 40mA
0.94
0.96
0.98
1.00
1.02
0.92
SEGMENT SOURCE CURRENT
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
5.04.54.03.53.02.5 5.5
MAX6955 toc05
VLED = 1.8V
1V/div
200µs/div
MAX6954 toc06
O0
O18
WAVEFORM AT PINS O0 AND O18,
MAXIMUM INTENSITY
0V
0V
GPIO SINK CURRENT
vs. TEMPERATURE
MAX 6955 toc07
TEMPERATURE (°C)
GPIO SINK CURRENT (mA)
110805020-10
5
10
15
20
25
30
35
40
45
0
-40
VCC = 5.5V
VCC = 3.3V
VCC = 2.5V
OUTPUT = LOW
VPORT = 0.6V
400µs/div
KEY_A: 1V/div
IRQ: 2V/div
MAX6954 toc09
KEY_A
0V
0V
IRQ
KEY-SCAN OPERATION
(KEY_A AND IRQ)
Typical Operating Characteristics
(V+ = 3.3V, LED forward voltage = 2.4V, Typical Application Circuit, TA= +25°C, unless otherwise noted.)
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 6www.maximintegrated.com
Detailed Description
The MAX6955 is a serially interfaced display driver that
can drive up to 16 digits 7-segment, 8 digits 14-seg-
ment, 8 digits 16-segment, 128 discrete LEDs, or a
combination of these display types. Table 1 shows the
drive capability of the MAX6955 for monocolor and
bicolor displays.
The MAX6955 includes 104-character ASCII font maps
for 14-segment and 16-segment displays, as well as
the hexadecimal font map for 7-segment displays. The
characters follow the standard ASCII font, with the
addition of the following common symbols: £, €, ¥, °, µ,
±, ↑, and ↓. Seven bits represent the 104-character
font map; an 8th bit is used to select whether the deci-
mal point (DP) is lit. Seven-segment LED digits can be
controlled directly or use the hexadecimal font. Direct
segment control allows the MAX6955 to be used to
drive bar graphs and discrete LED indicators.
Tables 2, 3, and 4 list the connection schemes for 16-,
14-, and 7-segment digits, respectively. The letters in
Tables 2, 3, and 4 correspond to the segment labels
shown in Figure 1. (For applications that require mixed
display types, see Tables 38–41.)
Serial Interface
Serial Addressing
The MAX6955 operates as a slave that sends and
receives data through an I2C-compatible 2-wire inter-
face. The interface uses a serial data line (SDA) and a
Pin Description
PIN
SSOP TQFN-EP NAME FUNCTION
1, 2,
34, 35
36, 37,
33, 34 P0–P3
General-Purpose I/O Ports (GPIOs). GPIO can be configured as logic inputs or open-drain
outputs. Enabling key scanning configures some or all ports P0–P3 as key-switch matrix inputs
with internal pullup (Key_A through Key_D).
3 38 AD0 Address Input 0. Sets device slave address. Connect to GND, V+, SCL, or SDA to give four
logic combinations. See Table 5.
4 39 SDA I2C-Compatible Serial Data I/O
5 40 SCL I2C-Compatible Serial Clock Input
6 1 AD1 Address Input 1. Sets device slave address. Connect to GND, V+, SCL, or SDA to give four
logic combinations. See Table 5.
7–15,
22–31
2–10,
21–30 O0–O18
Digit/Segment Drivers. When acting as digit drivers, outputs O0 to O7 sink current from the
display common cathodes. When acting as segment drivers, O0 to O18 source current to the
display anodes. O0 to O18 are high impedance when not being used as digit or segment
drivers.
16, 18 12, 13, 15 GND Ground
17 14 ISET Segment Current Setting. Connect ISET to GND through series resistor RSET to set the peak
current.
19, 21 16, 18, 19 V+ Positive Supply Voltage. Bypass V+ to GND with a 47µF bulk capacitor and a 0.1µF ceramic
capacitor.
20 17 OSC Multiplex Clock Input. To use internal oscillator, connect capacitor CSET from OSC to GND.
To use external clock, drive OSC with a 1MHz to 8MHz CMOS clock.
32 31 BLINK Blink Clock Output. Output is open drain.
33 32 OSC_OUT Clock Output. OSC_OUT is a buffered clock output to allow easy blink synchronization of
multiple MAX6955s. Output is push-pull.
36 35 P4/IRQ General-Purpose I/O Port. Also functions as IRQ output when key scanning is enabled.
— 11, 20 N.C. Not Internally Connected
—— EP
Exposed Paddle. Internally connected to GND. Connect to a large ground plane to improve
thermal performance.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 7www.maximintegrated.com
serial clock line (SCL) to achieve bidirectional commu-
nication between master(s) and slave(s). A master (typ-
ically a microcontroller) initiates all data transfers to and
from the MAX6955, and generates the SCL clock that
synchronizes the data transfer (Figure 2).
The MAX6955 SDA line operates as both an input and
an open-drain output. A pullup resistor, typically 4.7kΩ,
is required on the SDA. The MAX6955 SCL line oper-
ates only as an input. A pullup resistor, typically 4.7kΩ,
is required on SCL if there are multiple masters on the
2-wire interface, or if the master in a single-master sys-
tem has an open-drain SCL output.
Each transmission consists of a START condition
(Figure 3) sent by a master, followed by the MAX6955
7-bit slave address plus R/Wbit (Figure 4), a register
address byte, 1 or more data bytes, and finally a STOP
condition (Figure 3).
Start and Stop Conditions
Both SCL and SDA remain high when the interface is
not busy. A master signals the beginning of a transmis-
sion with a START (S) condition by transitioning SDA
from high to low while SCL is high. When the master
has finished communicating with the slave, it issues a
STOP (P) condition by transitioning the SDA from low to
high while SCL is high. The bus is then free for another
transmission (Figure 3).
Bit Transfer
One data bit is transferred during each clock pulse.
The data on the SDA line must remain stable while SCL
is high (Figure 5).
Acknowledge
The acknowledge bit is a clocked 9th bit that the recipient
uses to handshake receipt of each byte of data (Figure 6).
Thus, each byte transferred effectively requires 9 bits. The
master generates the 9th clock pulse, and the recipient
pulls down SDA during the acknowledge clock pulse, such
that the SDA line is stable low during the high period of the
clock pulse. When the master is transmitting to the
MAX6955, the MAX6955 generates the acknowledge bit
because the MAX6955 is the recipient. When the
MAX6955 is transmitting to the master, the master gener-
ates the acknowledge bit because the master is the recipi-
ent.
Slave Address
The MAX6955 has a 7-bit-long slave address (Figure
4). The eighth bit following the 7-bit slave address is
the R/Wbit. It is low for a write command, high for a
read command.
The first 3 bits (MSBs) of the MAX6955 slave address
are always 110. Slave address bits A3, A2, A1, and A0
are selected by the address input pins AD1 and AD0.
These two input pins can be connected to GND, V+,
SDA, or SCL. The MAX6955 has 16 possible slave
addresses (Table 5) and therefore a maximum of 16
MAX6955 devices can share the same interface.
DISPLAY TYPE
7 SEGMENT
(16-CHARACTER
HEXADECIMAL FONT)
14 SEGMENT/
16 SEGMENT
(104-CHARACTER ASCII FONT MAP)
DISCRETE LEDs
(DIRECT CONTROL)
Monocolor 16 8 128
Bicolor 8 4 64
Table 1. MAX6955 Drive Capability
1dp 2dp
fb
ec
d2
a1
i
l
g1 g2
hj
mk
a2
d1
dp dp
1a
1g
1f 1b
1e 1c
1d
2a
2g
2f 2b
2e 2c
2d
fb
ec
d
a
i
l
g1 g2
hj
mk
Figure 1. Segment Labeling for 7-Segment Display, 14-Segment Display, and 16-Segment Display
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 8www.maximintegrated.com
Message Format for Writing
A write to the MAX6955 comprises the transmission of
the MAX6955’s slave address with the R/Wbit set to
zero, followed by at least 1 byte of information. The first
byte of information is the command byte, which deter-
mines which register of the MAX6955 is to be written by
the next byte, if received. If a STOP condition is detect-
ed after the command byte is received, then the
MAX6955 takes no further action (Figure 7) beyond
storing the command byte.
Any bytes received after the command byte are data
bytes. The first data byte goes into the internal register of
the MAX6955 selected by the command byte (Figure 8).
If multiple data bytes are transmitted before a STOP
condition is detected, these bytes are generally stored
in subsequent MAX6955 internal registers because the
command byte address generally autoincrements
(Table 6) (Figure 9).
DIGIT O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 O12 O13 O14 O15 O16 O17 O18
0CCO— a1a2 b c d1d2 e f g1g2 h i j k l m dp
1 — CC1 a1 a2 b c d1 d2 e f g1 g2 h i j k l m dp
2 a1a2CC2— b c d1d2 e f g1g2 h i j k l m dp
3 a1 a2 — CC3 b c d1 d2 e f g1 g2 h i j k l m dp
4 a1a2 b cCC4—d1d2 e f g1g2 h i j k l m dp
5 a1 a2 b c — CC5 d1 d2 e f g1 g2 h i j k l m dp
6 a1 a2 b c d1 d2 CC6 — e f g1 g2 h i j k l m dp
7 a1 a2 b c d1 d2 — CC7 e f g1 g2 h i j k l m dp
DIGIT O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 O12 O13 O14 O15 O16 O17 O18
0 CCO — a — b c d — e f g1 g2 h i j k l m dp
1 — CC1 a — b c d — e f g1 g2 h i j k l m dp
2 a — CC2 — b c d — e f g1 g2 h i j k l m dp
3 a — — CC3 b c d — e f g1 g2 h i j k l m dp
4 a—b cCC4—d—e fg1g2h i j k l mdp
5 a — b c — CC5 d — e f g1 g2 h i j k l m dp
6 a—b c d—CC6—e fg1g2h i j k l mdp
7 a — b c d — — CC7 e f g1 g2 h i j k l m dp
Table 2. Connection Scheme for Eight 16-Segment Digits
Table 3. Connection Scheme for Eight 14-Segment Digits
DIGIT O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 O12 O13 O14 O15 O16 O17 O18
0, 0a CC0 — 1a — 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
1, 1a — CC1 1a — 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
2, 2a 1a — CC2 — 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
3, 3a 1a — — CC3 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
4, 4a 1a — 1b 1c CC4 — 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
5, 5a 1a — 1b 1c — CC5 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
6, 6a1a—1b1c1d1dpCC6— 1e 1f 1g2a2b2c2d2e 2f 2g2dp
7, 7a 1a — 1b 1c 1d 1dp — CC7 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
Table 4. Connection Scheme for Sixteen 7-Segment Digits
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 9www.maximintegrated.com
SDA
START CONDITION STOP CONDITION
SCL
SP
SDA
SCL MSBSTART
110A3 A2 A1 A0 R/W
LSB
ACK
Figure 3. Start and Stop Conditions
Figure 4. Slave Address
SDA
tLOW
tBUF
tSU, DAT tSU, STA
tHD, STA tSU, STO
tHD, DAT
tHIGH
tRtF
SCL
START
CONDITION
START
CONDITION
STOP
CONDITION
REPEATED START
CONDITION
tHD, STA
Figure 2. 2-Wire Serial Interface Timing Details
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 10www.maximintegrated.com
Message Format for Reading
The MAX6955 is read using the MAX6955’s internally
stored command byte as address pointer, the same
way the stored command byte is used as address
pointer for a write. The pointer generally autoincrements
after each data byte is read using the same rules as for
a write (Table 6). Thus, a read is initiated by first config-
uring the MAX6955’s command byte by performing a
write (Figure 7). The master can now read n consecu-
tive bytes from the MAX6955, with the first data byte
being read from the register addressed by the initial-
ized command byte (Figure 9). When performing read-
after-write verification, reset the command byte’s
address because the stored byte address generally is
autoincremented after the write (Table 6).
Operation with Multiple Masters
If the MAX6955 is operated on a 2-wire interface with
multiple masters, a master reading the MAX6955
should use a repeated start between the write, which
sets the MAX6955’s address pointer, and the read(s)
that takes the data from the location(s). This is because
it is possible for master 2 to take over the bus after
master 1 has set up the MAX6955’s address pointer but
before master 1 has read the data. If master 2 subse-
quently changes the MAX6955’s address pointer, then
master 1’s delayed read may be from an unexpected
location.
Command Address Autoincrementing
Address autoincrementing allows the MAX6955 to be
configured with the shortest number of transmissions by
minimizing the number of times the command byte
needs to be sent. The command address or the font
pointer address stored in the MAX6955 generally incre-
ments after each data byte is written or read (Table 6).
To utilize the autoincrement read cycle feature, the mas-
ter clocks SCL after the first data byte is read, and the
MAX6955 continues sending data, incrementing the
pointer after each byte is sent. A not-acknowledge or
stop condition halts autoincrement.
Digit Type Registers
The MAX6955 uses 32 digit registers to store the char-
acters that the user wishes to display. These digit regis-
ters are implemented with two planes, P0 and P1. Each
digit is represented by 2 bytes of memory, 1 byte in
plane P0 and the other in plane P1. The digit registers
are mapped so that a digit’s data can be updated in
plane P0, plane P1, or both planes at the same time
(Table 7).
If the blink function is disabled through the Blink Enable
Bit E (Table 20) in the configuration register, then the
digit register data in plane P0 is used to multiplex the
display. The digit register data in P1 is not used. If the
blink function is enabled, then the digit register data in
both plane P0 and plane P1 are alternately used to mul-
tiplex the display. Blinking is achieved by multiplexing
the LED display using data plane P0 and plane P1 on
alternate phases of the blink clock (Table 21).
COMMAND BYTE
ADDRESS RANGE AUTOINCREMENT BEHAVIOR
x0000000 to x0001100 Command byte address autoincrements after byte read or written.
x0001101 Factory reserved; do not write this register.
x0001111 to x1111110 Command byte address autoincrements after byte read or written.
x1111111 Command byte address remains at x1111111 after byte read or written.
Table 5. MAX6955 Address Map
Table 6. Command Address Autoincrement Rules
PIN CONNECTION DEVICE ADDRESS
AD1 AD0 A6A5A4A3A2A1A0
GND GND1100000
GND V+ 1100001
GND SDA 1100010
GND SCL 1100011
V+ GND1100100
V+ V+ 1100101
V+ SDA 1100110
V+ SCL 1100111
SDA GND1101000
SDA V+ 1101001
SDA SDA 1101010
SDA SCL 1101011
SCL GND1101100
SCL V+ 1101101
SCL SDA 1101110
SCL SCL 1101111
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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The data in the digit registers does not control the digit
segments directly for 14- and 16-segment displays.
Instead, the register data is used to address a charac-
ter generator that stores the data for the 14- and 16-
segment fonts (Tables 8 and 9). The lower 7 bits of the
digit data (D6 to D0) select the character from the font.
The most significant bit of the register data (D7) con-
trols the DP segment of the digits; it is set to 1 to light
DP, and to zero to leave DP unlit (Table 10).
For 7-segment displays, the digit plane data register
can be used to address a character generator, which
contains the data of a 16-character font containing the
hexadecimal font. The decode mode register can be
used to disable the character generator and allow the
segments to be controlled directly. Table 11 shows the
one-to-one pairing of each data bit to the appropriate
segment line in the digit plane data registers. The hexa-
decimal font is decoded according to Table 12.
The digit-type register configures the display driver for
various combinations of 14-segment digits, 16-segment
digits, and/or pairs, or 7-segment digits. The function of
this register is to select the appropriate font for each
digit and route the output of the font to the appropriate
MAX6955 driver output pins. The MAX6955 has four
digit drive slots. A slot can be filled with various combi-
nations of monocolor and bicolor 16-segment displays,
14-segment displays, or two 7-segment displays. Each
pair of bits in the register corresponds to one of the four
digit drive slots, as shown in Table 13. Each bit also cor-
responds to one of the eight common-cathode digit
drive outputs, CC0 to CC7. When using bicolor digits,
the anode connections for the two digits within a slot are
always the same. This means that a slot correctly drives
two monocolor or one bicolor 14- or 16-segment digit.
The digit type register can be written, but cannot be
read. Examples of configuration settings required for
some display digit combinations are shown in Table 14.
7-Segment Decode-Mode Register
In 7-segment mode, the hexadecimal font can be dis-
abled (Table 15). The decode-mode register selects
between hexadecimal code or direct control for each of
eight possible pairs of 7-segment digits. Each bit in the
register corresponds to one pair of digits. The digit
pairs are {digit 0, digit 0a} through {digit 7, digit 7a}.
Disabling decode mode allows direct control of the 16
LEDs of a dual 7-segment display. Direct control mode
can also be used to drive a matrix of 128 discrete LEDs.
A logic high selects hexadecimal decoding, while a
logic low bypasses the decoder. When direct control is
selected, the data bits D7 to D0 correspond to the seg-
ment lines of the MAX6955. Write x0010000 to blank all
segments in hexadecimal decode mode.
Display Blink Mode
The display blinking facility, when enabled, makes the
driver flip automatically between displaying the digit
register data in planes P0 and P1. If the digit register
data for any digit is different in the two planes, then that
digit appears to flip between two characters. To make a
character appear to blink on or off, write the character
to one plane, and use the blank character (0x20) for the
other plane. Once blinking has been configured, it con-
tinues automatically without further intervention.
Blink Speed
The blink speed is determined by the frequency of the
multiplex clock, OSC, and by the setting of the Blink
Rate Selection Bit B (Table 19) in the configuration reg-
ister. The Blink Rate Selection Bit B sets either fast or
slow blink speed for the whole display.
Initial Power-Up
On initial power-up, all control registers are reset, the
display is blanked, intensities are set to minimum, and
shutdown is enabled (Table 16).
Configuration Register
The configuration register is used to enter and exit shut-
down, select the blink rate, globally enable and disable
the blink function, globally clear the digit data, select
between global or digit-by-digit control of intensity, and
reset the blink timing (Tables 17–20 and 22–25).
The configuration register contains 7 bits:
• S bit selects shutdown or normal operation
(read/write).
• B bit selects the blink rate (read/write).
• E bit globally enables or disables the blink function
(read/write).
• T bit resets the blink timing (data is not stored—tran-
sient bit).
• R bit globally clears the digit data for both planes P0
and P1 for ALL digits (data is not stored—transient bit).
• I bit selects between global or digit-by-digit control
of intensity (read/write).
• P bit returns the current phase of the blink timing
(read only—a write to this bit is ignored).
Character Generator Font Mapping
The font is composed of 104 characters in ROM. The
lower 7 bits of the 8-bit digit register represent the char-
acter selection. The most significant bit, shown as x in
the ROM map of Tables 8 and 9, is 1 to light the DP
segment and zero to leave the DP segment unlit.
The character map follows the standard ASCII font for
96 characters in the x0101000 through x1111111
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 12www.maximintegrated.com
range. The first 16 characters of the 16-segment ROM
map cover 7-segment displays. These 16 characters
are numeric 0 to 9 and characters A to F (i.e., the hexa-
decimal set).
Multiplex Clock and Blink Timing
The OSC pin can be fitted with capacitor CSET to GND to
use the internal RC multiplex oscillator, or driven by an
external clock to set the multiplex clock frequency and
blink rate. The multiplex clock frequency determines the
frequency that the complete display is updated. With
OSC at 4MHz, each display digit is enabled for 200µs.
The internal RC oscillator uses an external resistor,
RSET, and an external capacitor, CSET, to set the oscil-
lator frequency. The suggested values of RSET (56kΩ)
and CSET (22pF) set the oscillator at 4MHz, which
makes the blink frequency 0.5Hz or 1Hz.
The external clock is not required to have a 50:50 duty
cycle, but the minimum time between transitions must
be 50ns or greater and the maximum time between
transitions must be 750ns.
The on-chip oscillator may be accurate enough for
applications using a single device. If an exact blink rate
is required, use an external clock ranging between
1MHz and 8MHz to drive OSC. The OSC inputs of multi-
ple MAX6955s can be connected to a common external
clock to make the devices blink at the same rate. The
relative blink phasing of multiple MAX6955s can be syn-
chronized by setting the T bit in the control register for
all the devices in quick succession. If the serial inter-
faces of multiple MAX6955s are daisy-chained by con-
necting the DOUT of one device to the DIN of the next,
then synchronization is achieved automatically by
updating the configuration register for all devices simul-
taneously. Figure 10 is the multiplex timing diagram.
OSC_OUT Output
The OSC_OUT output is a buffered copy of either the
internal oscillator clock or the clock driven into the OSC
pin if the external clock has been selected. The feature
is useful if the internal oscillator is used, and the user
wishes to synchronize other MAX6955s to the same
blink frequency. The oscillator is disabled while the
MAX6955 is in shutdown.
Scan-Limit Register
The scan-limit register sets how many 14-segment dig-
its or 16-segment digits or pairs of 7-segment digits are
displayed, from 1 to 8. A bicolor digit is connected as
two monocolor digits. The scan register also limits the
number of keys that can be scanned.
Since the number of scanned digits affects the display
brightness, the scan-limit register should not be used to
blank portions of the display (such as leading-zero sup-
pression). Table 26 shows the scan-limit register format.
Intensity Registers
Digital control of display brightness is provided and
can be managed in one of two ways: globally or individ-
ually. Global control adjusts all digits together.
Individual control adjusts the digits separately.
The default method is global brightness control, which
is selected by clearing the global intensity bit (I data bit
D6) in the configuration register. This brightness setting
applies to all display digits. The pulse-width modulator
is then set by the lower nibble of the global intensity
register, address 0x02. The modulator scales the aver-
age segment current in 16 steps from a maximum of
15/16 down to 1/16 of the peak current. The minimum
interdigit blanking time is set to 1/16 of a cycle. When
using bicolor digits, 256 color/brightness combinations
are available.
Individual brightness control is selected by setting the
global intensity bit (I data bit D6) in the configuration
register. The pulse-width modulator is now no longer
set by the lower nibble of the global intensity register,
address 0x02, and the data is ignored. Individual digital
control of display brightness is now provided by a sep-
arate pulse-width modulator setting for each digit. Each
digit is controlled by a nibble of one of the four intensity
registers: intensity10, intensity32, intensity54, and inten-
sity76 for all display types, plus intensity10a, intensi-
ty32a, intensity54a, and intensity76a for the extra eight
digits possible when 7-segment displays are used. The
data from the relevant register is used for each digit as
it is multiplexed. The modulator scales the average
segment current in 16 steps in exactly the same way as
global intensity adjustment.
Table 27 shows the global intensity register format. Table
28 shows individual segment intensity registers. Table 29
shows the even individual segment intensity format. Table
30 shows the odd individual segment intensity format.
GPIO and Key Scanning
The MAX6955 features five general-purpose input/out-
put (GPIO) ports: P0 to P4. These ports can be individ-
ually enabled as logic inputs or open-drain logic
outputs. The GPIO ports are not debounced when con-
figured as inputs. The ports can be read and the out-
puts set using the 2-wire interface.
Some or all of the five ports can be configured to per-
form key scanning of up to 32 keys. Ports P0 to P4 are
renamed Key_A, Key_B, Key_C, Key_D, and IRQ,
respectively, when used for key scanning. The full key-
scanning configuration is shown in Figure 11. Table 31
is the GPIO data register.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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ADDRESS (COMMAND BYTE)
REGISTER D15 D14 D13 D12 D11 D10 D9 D8 HEX CODE
No-Op X 0 0 0 0 0 0 0 0x00
Decode Mode X 0 0 0 0 0 0 1 0x01
Global Intensity X 0 0 0 0 0 1 0 0x02
Scan Limit X 0 0 0 0 0 1 1 0x03
Configuration X 0 0 0 0 1 0 0 0x04
GPIO Data X 0 0 0 0 1 0 1 0x05
Port Configuration X 0 0 0 0 1 1 0 0x06
Display Test X 0 0 0 0 1 1 1 0x07
Write KEY_A Mask
Read KEY_A Debounce X 0 0 0 1 0 0 0 0x08
Write KEY_B Mask
Read KEY_B Debounce X 0 0 0 1 0 0 1 0x09
Write KEY_C Mask
Read KEY_C Debounce X 0 0 0 1 0 1 0 0x0A
Write KEY_D Mask
Read KEY_D Debounce X 0 0 0 1 0 1 1 0x0B
Write Digit Type
Read KEY_A Pressed X 0 0 0 1 1 0 0 0x0C
Read KEY_B Pressed* X 0 0 0 1 1 0 1 0x0D
Read KEY_C Pressed* X 0 0 0 1 1 1 0 0x0E
Read KEY_D Pressed* X 0 0 0 1 1 1 1 0x0F
Intensity 10 X 0 0 1 0 0 0 0 0x10
Intensity 32 X 0 0 1 0 0 0 1 0x11
Intensity 54 X 0 0 1 0 0 1 0 0x12
Intensity 76 X 0 0 1 0 0 1 1 0x13
Intensity 10a (7 Segment Only) X 0 0 1 0 1 0 0 0x14
Intensity 32a (7 Segment Only) X 0 0 1 0 1 0 1 0x15
Intensity 54a (7 Segment Only) X 0 0 1 0 1 1 0 0x16
Intensity 76a (7 Segment Only) X 0 0 1 0 1 1 1 0x17
Digit 0 Plane P0 X 0 1 0 0 0 0 0 0x20
Digit 1 Plane P0 X 0 1 0 0 0 0 1 0x21
Digit 2 Plane P0 X 0 1 0 0 0 1 0 0x22
Digit 3 Plane P0 X 0 1 0 0 0 1 1 0x23
Digit 4 Plane P0 X 0 1 0 0 1 0 0 0x24
Digit 5 Plane P0 X 0 1 0 0 1 0 1 0x25
Digit 6 Plane P0 X 0 1 0 0 1 1 0 0x26
Digit 7 Plane P0 X 0 1 0 0 1 1 1 0x27
Digit 0a Plane P0 (7 Segment Only) X 0 1 0 1 0 0 0 0x28
Digit 1a Plane P0 (7 Segment Only) X 0 1 0 1 0 0 1 0x29
Digit 2a Plane P0 (7 Segment Only) X 0 1 0 1 0 1 0 0x2A
Digit 3a Plane P0 (7 Segment Only) X 0 1 0 1 0 1 1 0x2B
Table 7. Register Address Map
*
Do NOT write to register.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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ADDRESS (COMMAND BYTE)
REGISTER D15 D14 D13 D12 D11 D10 D9 D8 HEX CODE
Digit 4a Plane P0 (7 Segment Only) X 0 1 0 1 1 0 0 0x2C
Digit 5a Plane P0 (7 Segment Only) X 0 1 0 1 1 0 1 0x2D
Digit 6a Plane P0 (7 Segment Only) X 0 1 0 1 1 1 0 0x2E
Digit 7a Plane P0 (7 Segment Only) X 0 1 0 1 1 1 1 0x2F
Digit 0 Plane P1 X 1 0 0 0 0 0 0 0x40
Digit 1 Plane P1 X 1 0 0 0 0 0 1 0x41
Digit 2 Plane P1 X 1 0 0 0 0 1 0 0x42
Digit 3 Plane P1 X 1 0 0 0 0 1 1 0x43
Digit 4 Plane P1 X 1 0 0 0 1 0 0 0x44
Digit 5 Plane P1 X 1 0 0 0 1 0 1 0x45
Digit 6 Plane P1 X 1 0 0 0 1 1 0 0x46
Digit 7 Plane P1 X 1 0 0 0 1 1 1 0x47
Digit 0a Plane P1 (7 Segment Only) X 1 0 0 1 0 0 0 0x48
Digit 1a Plane P1 (7 Segment Only) X 1 0 0 1 0 0 1 0x49
Digit 2a Plane P1 (7 Segment Only) X 1 0 0 1 0 1 0 0x4A
Digit 3a Plane P1 (7 Segment Only) X 1 0 0 1 0 1 1 0x4B
Digit 4a Plane P1 (7 Segment Only) X 1 0 0 1 1 0 0 0x4C
Digit 5a Plane P1 (7 Segment Only) X 1 0 0 1 1 0 1 0x4D
Digit 6a Plane P1 (7 Segment Only) X 1 0 0 1 1 1 0 0x4E
Digit 7a Plane P1 (7 Segment Only) X 1 0 0 1 1 1 1 0x4F
Write Digit 0 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 0 0 0 0x60
Write Digit 1 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 0 0 1 0x61
Write Digit 2 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 0 1 0 0x62
Write Digit 3 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 0 1 1 0x63
Write Digit 4 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 1 0 0 0x64
Write Digit 5 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 1 0 1 0x65
Write Digit 6 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 1 1 0 0x66
Write Digit 7 Planes P0 and P1 with Same
Data, Reads as 0x00 X 1 1 0 0 1 1 1 0x67
Write Digit 0a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 0 0 0 0x68
Write Digit 1a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 0 0 1 0x69
Table 7. Register Address Map (continued)
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 15www.maximintegrated.com
One diode is required per key switch. Note that the for-
ward voltages of the diode and LED must exceed VIH
of P0–P3. If this condition is not met, the voltage input
to the port might be lower than the logic threshold and
keys will not be detected properly.
The MAX6955 can only scan the maximum 32 keys if
the scan-limit register is set to scan the maximum eight
digits. If the MAX6955 is driving fewer digits, then a
maximum of (4 x n) switches can be scanned, where n
is the number of digits set in the scan-limit register. For
example, if the MAX6955 is driving four 14-segment
digits, cathode drivers O0 to O3 are used. Only 16 keys
can be scanned in this configuration; the switches
shown connected to O4 through O7 are not read.
If the user wishes to scan fewer than 32 keys, then
fewer scan lines can be configured for key scanning.
The unused Key_x ports are released back to their orig-
inal GPIO functionality. If key scanning is enabled,
regardless of the number of keys being scanned,
P4/IRQ is always configured as IRQ (Table 32).
The key-scanning circuit utilizes the LEDs’ common-
cathode driver outputs as the key-scan drivers. O0 to
O7 go low for nominally 200µs (with OSC = 4MHz) in
turn as the displays are multiplexed. By varying the
oscillator frequency, the debounce time changes,
though key scanning still functions. Key_x inputs have
internal pullup resistors that allow the key condition to
be tested. The Key_x input is low during the appropri-
ate digit multiplex period when the key is pressed. The
timing diagram of Figure 12 shows the normal situation
where all eight LED cathode drivers are used.
ADDRESS (COMMAND BYTE)
REGISTER D15 D14 D13 D12 D11 D10 D9 D8 HEX CODE
Write Digit 2a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 0 1 0 0x6A
Write Digit 3a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 0 1 1 0x6B
Write Digit 4a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 1 0 0 0x6C
Write Digit 5a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 1 0 1 0x6D
Write Digit 6a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 1 1 0 0x6E
Write Digit 7a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00 X 1 1 0 1 1 1 1 0x6F
Table 7. Register Address Map (continued)
Note: Unused register bits read as zero.
SDA
DATA LINE STABLE,
DATA VALID
CHANGE OF DATA
ALLOWED
SCL
Figure 5. Bit Transfer
1
SCL
START CONDITION
SDA
BY TRANSMITTER
SDA
BY RECEIVER
S
28 9
CLOCK PULSE FOR ACKNOWLEDGMENT
Figure 6. Acknowledge
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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Each key press is scanned twice in a 25.6ms time peri-
od with a nominal oscillator frequency of 4MHz, as
shown in Figure 12. In the first key test period of 1.6ms,
input level at ports P0–P3 (Key_A, Key_B, Key_C, and
Key_D) are examined in conjunction with the signal-low
period of ports O0–O7 to see if any key is pressed. If
pressed, the corresponding key pressed register bit is
set. In the second key test period of 1.6ms, input level
at ports P0–P3 are examined again (debounce) to see if
the key is still pressed. If still pressed, the correspond-
ing debounce register bit is set. The debounce time
between key tests is 12.8ms.
Port Configuration Register
The port configuration register selects how the five port
pins are used. The port configuration register format is
described in Table 33.
Key Mask Registers
The Key_A Mask, Key_B Mask, Key_C Mask, and
Key_D Mask write-only registers (Table 34) configure
the key-scanning circuit to cause an interrupt only when
selected (masked) keys have been debounced. Each
bit in the register corresponds to one key switch. The bit
is clear to disable interrupt for the switch, and set to
enable interrupt. Keys are always scanned (if enabled
through the port configuration register), regardless of
the setting of these interrupt bits, and the key status is
stored in the appropriate Key_x pressed register.
S
A0
SLAVE ADDRESS COMMAND BYTE
ACKNOWLEDGE FROM MAX6955
R/W ACKNOWLEDGE FROM MAX6955
D15 D14 D13 D12 D11 D10 D 9 D 8
COMMAND BYTE IS STORED ON RECEIPT OF STOP CONDITION
A P
Figure 7. Command Byte Received
AP0SLAVE ADDRESS
COMMAND BYTE
DATA BYTE
ACKNOWLEDGE FROM MAX6955
R/W 1 BYTE
AUTOINCREMENT MEMORY WORD ADDRESS
ACKNOWLEDGE FROM MAX6955 ACKNOWLEDGE FROM MAX6955
D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6
HOW CONTROL BYTE AND DATA BYTE MAP INTO
MAX6955's REGISTERS
S
AA
Figure 8. Command and Single Data Byte Received
AP0SLAVE ADDRESS
COMMAND BYTE
DATA BYTE
ACKNOWLEDGE FROM MAX6955
R/W n BYTE
AUTOINCREMENT MEMORY WORD ADDRESS
ACKNOWLEDGE FROM MAX6955 ACKNOWLEDGE FROM MAX6955
D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6
HOW CONTROL BYTE AND DATA BYTE MAP INTO
MAX6955's REGISTERS
S
AA
Figure 9. n Data Bytes Received
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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DIGIT 1
ONE COMPLETE 1.6ms MULTIPLEX CYCLE AROUND 8 DIGITS
DIGIT 0's 200µs MULTIPLEX TIMESLOT
DIGIT 0
200µs
DIGIT 2 DIGIT 3 DIGIT 4 DIGIT 5 DIGIT 6 DIGIT 7
START OF
NEXT CYCLE
LOW
2/16TH
1/16TH
(MIN ON)
HIGH-Z
HIGH-Z
LOW
3/16TH HIGH-Z
LOW
4/16TH HIGH-Z
LOW
5/16TH HIGH-Z
LOW
6/16TH HIGH-Z
LOW
7/16TH HIGH-Z
LOW
8/16TH HIGH-Z
LOW
9/16TH HIGH-Z
LOW
10/16TH HIGH-Z
LOW
11/16TH HIGH-Z
LOW
12/16TH HIGH-Z
LOW
13/16TH HIGH-Z
LOW
14/16TH HIGH-Z
LOW
15/16TH HIGH-Z
LOW
15/16TH HIGH-Z
(MAX ON)
HIGH-Z
HIGH-Z
CURRENT SOURCE ENABLED MINIMUM 12.5µs INTERDIGIT BLANKING INTERVAL
HIGH-Z
ANODE (LIT)
DIGIT 0 CATHODE
DRIVER INTENSITY
SETTINGS
ANODE (UNLIT)
Figure 10. Multiplex Timing Diagram (OSC = 4MHz)
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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LED OUTPUT 00
LED OUTPUT 01
LED OUTPUT 02
LED OUTPUT 03
LED OUTPUT 04
LED OUTPUT 05
LED OUTPUT 06
LED OUTPUT 07
FIRST KEY TEST
PERIOD
START END
SECOND KEY TEST
PERIOD
(DEBOUNCE)
START START OF NEXT KEY-SCAN CYCLE
INTERRUPT ASSERTED IF PERIOD
DEBOUNCE REGISTER UPDATED
END
12.5µs TO 187.5µs DIGIT PERIOD
1.6ms MULTIPLEX CYCLE 1
12.8MS FIRST HALF KEY-SCAN CYCLE 12.8MS SECOND HALF KEY-SCAN CYCLE
A 25.6MS KEY-SCAN CYCLE
1.6ms MULTIPLEX CYCLE 2 1.6ms MULTIPLEX CYCLE 8 1.6ms MULTIPLEX CYCLE 1 1.6ms MULTIPLEX CYCLE 6
Figure 11. Key-Scanning Configuration
SW A0
SW A1
SW A2
SW A3
SW A4
SW A5
SW A6
SW A7
KEY_A (P0)
V
CC
LED OUTPUT O0
LED OUTPUT O1
LED OUTPUT O2
LED OUTPUT O3
LED OUTPUT O4
LED OUTPUT O5
LED OUTPUT O6
LED OUTPUT O7
KEY_B (P1)
KEY_C (P2)
KEY_D (P3)
IRQ (P4) MICROCONTROLLER INTERRUPT
SW B0
SW B1
SW B2
SW B3
SW B4
SW B5
SW B6
SW B7
SW C0
SW C1
SW C2
SW C3
SW C4
SW C5
SW C6
SW C7
SW D0
LED0
LED SEGMENT IS OPTIONAL AND
BASED ON APPLICATION.
SW D1
SW D2
SW D3
SW D4
SW D5
SW D6
SW D7
LED1
LED2
LED3
LED4
LED5
Figure 12. Key-Scan Timing Diagram
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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Key Debounced Registers
The Key_A debounced, Key_B debounced, Key_C
debounced, and Key_D debounced read-only registers
(Table 35) show which keys have been detected as
debounced by the key-scanning circuit.
Each bit in the register corresponds to one key switch.
The bit is set if the switch has been correctly
debounced since the register was read last. Reading a
debounced register clears that register (after the data
has been read) so that future keys pressed can be
identified. If the debounced registers are not read, the
key-scan data accumulates. However, as there is no
FIFO in the MAX6955, the user is not able to determine
key order, or whether a key has been pressed more
than once, unless the debounced key status registers
are read after each interrupt, and before the next key-
scan cycle.
Reading any of the four debounced registers clears the
P4/IRQ output. If a key is pressed and held down, the
key is reported as debounced (and IRQ issued) only
once. The key must be detected as released by the key-
scanning circuit, before it debounces again. If the
debounced registers are being read in response to the
P4/IRQ being asserted, then the user should generally
read all four registers to ensure that all the keys that were
detected by the key-scanning circuit are discovered.
Key Pressed Registers
The Key_A pressed, Key_B pressed, Key_C pressed,
and Key_D pressed read-only registers (Table 36)
show which keys have been detected as pressed by
the key-scanning circuit during the last test.
Each bit in the register corresponds to one key switch.
The bit is set if the switch has been detected as
pressed by the key-scanning circuit during the last test.
The bit is cleared if the switch has not been detected
as pressed by the key-scanning circuit during the last
test. Reading a pressed register does not clear that
register or clear the P4/IRQ output.
Display Test Register
The display test register (Table 37) operates in two
modes: normal and display test. Display test mode
turns all LEDs on (including DPs) by overriding, but not
altering, all controls and digit registers (including the
shutdown register), except for the digit-type register
and the GPIO configuration register. The duty cycle,
while in display test mode, is 7/16 (see the
Choosing
Supply Voltage to Minimize Power Dissipation
section).
External Components RSET and
CSET to Set Oscillator Frequency and
Peak Segment Current
The RC oscillator uses an external resistor, RSET, and
an external capacitor, CSET, to set the frequency, fOSC.
The allowed range of fOSC is 1MHz to 8MHz. RSET also
sets the peak segment current. The recommended val-
ues of RSET and CSET set the oscillator to 4MHz, which
makes the blink frequencies selectable between 0.5Hz
and 1Hz. The recommended value of RSET also sets the
peak current to 40mA, which makes the segment cur-
rent adjustable from 2.5mA to 37.5mA in 2.5mA steps.
ISEG = KL/RSET mA
fOSC = KF/(RSET x CSET) MHz
where:
KL= 2240
KF= 10K (typ)
RSET = external resistor in kΩ
CSET = external capacitor in pF
CSTRAY = stray capacitance from OSC pin to GND in pF
The recommended value of RSET is 56kΩand the rec-
ommended value of CSET is 22pF.
The recommended value of RSET is the minimum
allowed value, since it sets the display driver to the
maximum allowed peak segment current. RSET can be
set to a higher value to set the segment current to a
lower peak value where desired. The user must also
ensure that the peak current specifications of the LEDs
connected to the driver are not exceeded.
The effective value of CSET includes not only the actual
external capacitor used, but also the stray capacitance
from OSC to GND. This capacitance is usually in the
1pF to 30pF range, depending on the layout used.
Applications Information
Driving Bicolor LEDs
Bicolor digits group a red and a green die together for
each display element, so that the element can be lit red
or green (or orange), depending on which die (or both)
is lit. The MAX6955 allows each segment’s current to
be set individually from the 1/16th (minimum current
and LED intensity) to 15/16th (maximum current and
LED intensity), as well as off (zero current). Thus, a
bicolor (red-green) segment pair can be set to 256
color/intensity combinations.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 20www.maximintegrated.com
Choosing Supply Voltage to Minimize
Power Dissipation
The MAX6955 drives a peak current of 40mA into LEDs
with a 2.2V forward-voltage drop when operated from a
supply voltage of at least 3.0V. The minimum voltage
drop across the internal LED drivers is therefore (3.0V -
2.2V) = 0.8V. If a higher supply voltage is used, the dri-
ver absorbs a higher voltage, and the driver’s power
dissipation increases accordingly. However, if the LEDs
used have a higher forward-voltage drop than 2.2V, the
supply voltage must be raised accordingly to ensure
that the driver always has at least 0.6V of headroom.
The voltage drop across the drivers with a nominal 5V
supply (5.0V - 2.2V) = 2.8V is nearly 3 times the drop
across the drivers with a nominal 3.3V supply (3.3V -
2.2V) = 1.1V. In most systems, consumption is an
important design criterion, and the MAX6955 should be
operated from the system’s 3.3V nominal supply. In
other designs, the lowest supply voltage may be 5V.
The issue now is to ensure the dissipation limit for the
MAX6955 is not exceeded. This can be achieved by
inserting a series resistor in the supply to the MAX6955,
ensuring that the supply decoupling capacitors are still
on the MAX6955 side of the resistor. For example, con-
sider the requirement that the minimum supply voltage
to a MAX6955 must be 3.0V, and the input supply
range is 5V ±5%. Maximum supply current is 35mA +
(40mA x 17) = 715mA. Minimum input supply voltage is
4.75V. Maximum series resistor value is (4.75V -
3.0V)/0.715A = 2.44Ω. We choose 2.2Ω±5%. Worst-
case resistor dissipation is at maximum toleranced
resistance, i.e., (0.715A) 2 x (2.2Ωx 1.05) = 1.18W. The
maximum MAX6955 supply voltage is at maximum
input supply voltage and minimum toleranced resis-
tance, i.e., 5.25V - (0.715A x 2.2Ωx 0.95) = 3.76V.
Low-Voltage Operation
The MAX6955 works over the 2.7V to 5.5V supply
range. The minimum useful supply voltage is deter-
mined by the forward-voltage drop of the LEDs at the
peak current ISEG, plus the 0.8V headroom required by
the driver output stages. The MAX6955 correctly regu-
lates ISEG with a supply voltage above this minimum
voltage. If the supply drops below this minimum volt-
age, the driver output stages can brown out, and be
unable to regulate the current correctly. As the supply
voltage drops further, the LED segment drive current
becomes effectively limited by the output driver's on-
resistance, and the LED drive current drops. The char-
acteristics of each individual LED in a display digit are
well matched, so the result is that the display intensity
dims uniformly as supply voltage drops out of regula-
tion and beyond.
Computing Power Dissipation
The upper limit for power dissipation (PD) for the
MAX6955 is determined from the following equation:
PD= (V+ x 35mA) + (V+ - VLED) (DUTY x ISEG x N)
where:
V+ = supply voltage
DUTY = duty cycle set by intensity register
N = number of segments driven (worst case is 17)
VLED = LED forward voltage at ISEG
ISEG = segment current set by RSET
PD= Power dissipation, in mW if currents are in mA
Dissipation example:
ISEG = 30mA, N = 17, DUTY = 15/16,
VLED = 2.4V at 30mA, V+ = 3.6V
PD= 3.6V (35mA) + (3.6V - 2.4V)(15/16 x
30mA x 17) = 0.700W
Thus, for a 36-pin SSOP package (TJA = 1/0.0118 =
+85°C/W from Operating Ratings), the maximum
allowed ambient temperature TAis given by:
TJ(MAX) = TA+ (PDx TJA) = +150°C
= TA+ (0.700 x +85°C/W)
So TA= +90.5°C. Thus, the part can be operated safely
at a maximum package temperature of +85°C.
Power Supplies
The MAX6955 operates from a single 2.7V to 5.5V
power supply. Bypass the power supply to GND with a
0.1µF capacitor as close to the device as possible. Add
a 47µF capacitor if the MAX6955 is not close to the
board’s input bulk decoupling capacitor.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 21www.maximintegrated.com
x000 x010 x011 x100 x101 x110 x111x001
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
MSB
LSB
Table 8. 16-Segment Display Font Map
x000 x010 x011 x100 x101 x110 x111x001
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
MSB
LSB
Table 9. 14-Segment Display Font Map
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 22www.maximintegrated.com
REGISTER DATA
MODE
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
14-segment or 16-segment mode, writing digit data
to use font map data with decimal place unlit
0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F
0 Bits D6 to D0 select font characters 0 to 127
14-segment or 16-segment mode, writing digit data
to use font map data with decimal place lit
0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F
1 Bits D6 to D0 select font characters 0 to 127
7-segment decode mode, DP unlit
0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F
0 0 0 0 D3 to D0
7-segment decode mode, DP lit
0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F
1 0 0 0 D3 to D0
7-segment no-decode mode
0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F
Direct control of 8 segments
Table 10. Digit Plane Data Register Format
REGISTER DATA
MODE ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Segment Line
0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F
dp a b c d e f g
Table 11. Segment Decoding for 7-Segment Displays
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 23www.maximintegrated.com
REGISTER
DATA ON SEGMENTS = 1
7-SEGMENT
CHARACTER
D7* D6, D5,
D4 D3 D2 D1 D0 DP* A B C D E F G
0 — X 0 0 0 0 — 111111 0
1 — X 0 0 0 1 — 011000 0
2 — X 0 0 1 0 — 110110 1
3 — X 0 0 1 1 — 111100 1
4 — X 0 1 0 0 — 011001 1
5 — X 0 1 0 1 — 101101 1
6 — X 0 1 1 0 — 101111 1
7 — X 0 1 1 1 — 111000 0
8 — X 1 0 0 0 — 111111 1
9 — X 1 0 0 1 — 111101 1
A — X 1 0 1 0 — 111011 1
B — X 1 0 1 1 — 001111 1
C — X 1 1 0 0 — 100111 0
D — X 1 1 0 1 — 011110 1
E — X 1 1 1 0 — 100111 1
F — X 1 1 1 1 — 100011 1
Table 12. 7-Segment Segment Mapping Decoder for Hexadecimal Font
REGISTER DATA
DIGIT-TYPE
REGISTER
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Output Drive Line CC7 CC6 CC5 CC4 CC3 CC2 CC1 CC0
Slot Identification 0x0C Slot 4 Slot 3 Slot 2 Slot 1
Table 13. Digit-Type Register
*
The decimal point is set by bit D7 = 1.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 24www.maximintegrated.com
REGISTER DATA
DECODE
MODE
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
HEX
CODE
No decode for digit pairs 7 to 0. 0x01 00000000 0x00
Hexadecimal decode for digit pair 0,
no decode for digit pairs 7 to 1. 0x01 00000001 0x01
Hexadecimal decode for digit pairs 2 to 0,
no decode for digit pairs 7 to 3. 0x01 00000111 0x07
Hexadecimal decode for digit pairs 7 to 0. 0x01 11111111 0xFF
Table 15. Decode-Mode Register Examples
REGISTER DATA
DIGIT-TYPE
REGISTER SETTING
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Digits 7 to 0 are 16-segment or 7-
segment digits. 0x0C 00000000
Digit 0 is a 14-segment digit,
digits 7 to 1 are 16-segment or 7-
segment digits.
0x0C 00000001
Digits 2 to 0 are 14-segment
digits, digits 7 to 3 are 16-
segment or 7-segment digits.
0x0C 00000111
Digits 7 to 0 are 14-segment
digits. 0x0C 11111111
Table 14. Example Configurations for Display Digit Combinations
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 25www.maximintegrated.com
REGISTER DATA
REGISTER POWER-UP
CONDITION
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Decode Mode Decode mode enabled 0x01 1 1 1 1 1 1 1 1
Global Intensity 1/16 (min on) 0x02 X XXX0000
Scan Limit Display 8 digits: 0, 1, 2, 3, 4, 5, 6, 7 0x03 X X X X X 1 1 1
Control Register Shutdown enabled, blink speed is
slow, blink disabled 0x04 0 0 X X 0 0 0 0
GPIO Data Outputs are low 0x05 X X X 0 0 0 0 0
Port Configuration No key scanning, P0 to P4 are all
inputs 0x06 0 0 0 1 1 1 1 1
Display Test Normal operation 0x07 X X X X XXX0
Key_A Mask None of the keys cause interrupt 0x08 0 0 0 0 0 0 0 0
Key_B Mask None of the keys cause interrupt 0x09 0 0 0 0 0 0 0 0
Key_C Mask None of the keys cause interrupt 0x0A 0 0 0 0 0 0 0 0
Key_D Mask None of the keys cause interrupt 0x0B 0 0 0 0 0 0 0 0
Digit Type All are 16 segment or 7 segment 0x0C 0 0 0 0 0 0 0 0
Intensity10 1/16 (min on) 0x10 0 0 0 0 0 0 0 0
Intensity32 1/16 (min on) 0x11 0 0 0 0 0 0 0 0
Intensity54 1/16 (min on) 0x12 0 0 0 0 0 0 0 0
Intensity76 1/16 (min on) 0x13 0 0 0 0 0 0 0 0
Intensity10a 1/16 (min on) 0x14 0 0 0 0 0 0 0 0
Intensity32a 1/16 (min on) 0x15 0 0 0 0 0 0 0 0
Intensity54a 1/16 (min on) 0x16 0 0 0 0 0 0 0 0
Intensity76a 1/16 (min on) 0x17 0 0 0 0 0 0 0 0
Digit 0 Blank digit, both planes 0x60 0 0 1 0 0 0 0 0
Digit 1 Blank digit, both planes 0x61 0 0 1 0 0 0 0 0
Digit 2 Blank digit, both planes 0x62 0 0 1 0 0 0 0 0
Digit 3 Blank digit, both planes 0x63 0 0 1 0 0 0 0 0
Digit 4 Blank digit, both planes 0x64 0 0 1 0 0 0 0 0
Digit 5 Blank digit, both planes 0x65 0 0 1 0 0 0 0 0
Digit 6 Blank digit, both planes 0x66 0 0 1 0 0 0 0 0
Digit 7 Blank digit, both planes 0x67 0 0 1 0 0 0 0 0
Digit 0a Blank digit, both planes 0x68 0 0 0 0 0 0 0 0
Digit 1a Blank digit, both planes 0x69 0 0 0 0 0 0 0 0
Digit 2a Blank digit, both planes 0x6A 0 0 0 0 0 0 0 0
Digit 3a Blank digit, both planes 0x6B 0 0 0 0 0 0 0 0
Digit 4a Blank digit, both planes 0x6C 0 0 0 0 0 0 0 0
Digit 5a Blank digit, both planes 0x6D 0 0 0 0 0 0 0 0
Digit 6a Blank digit, both planes 0x6E 0 0 0 0 0 0 0 0
Digit 7a Blank digit, both planes 0x6F 0 0 0 0 0 0 0 0
Key_A Debounced No key presses have been detected 0x08 0 0 0 0 0 0 0 0
Key_B Debounced No key presses have been detected 0x09 0 0 0 0 0 0 0 0
Key_C Debounced No key presses have been detected 0x0A 0 0 0 0 0 0 0 0
Key_D Debounced No key presses have been detected 0x0B 0 0 0 0 0 0 0 0
Key_A Pressed Keys are not pressed 0x0C 0 0 0 0 0 0 0 0
Key_B Pressed Keys are not pressed 0x0D 0 0 0 0 0 0 0 0
Key_C Pressed Keys are not pressed 0x0E 0 0 0 0 0 0 0 0
Key_D Pressed Keys are not pressed 0x0F 0 0 0 0 0 0 0 0
Table 16. Initial Power-Up Register Status
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
Configuration
Register P I RTEBXS
Table 17. Configuration Register
Format
REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
Shutdown P I R T E B X 0
Normal
Operation PIRTEBX1
Table 18. Shutdown Control
(S Data Bit DO) Format
REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
Slow blinking. Segments blink on for 1s, off for 1s with fOSC = 4MHz. P I R T E 0 X S
Fast blinking. Segments blink on for 0.5s, off for 0.5s with fOSC = 4MHz. P I R T E 1 X S
Table 19. Blink Rate Selection (B Data Bit D2) Format
REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
Blink function is disabled. P I R T 0 B X S
Blink function is enabled. P I R T 1 B X S
Table 20. Global Blink Enable/Disable (E Data Bit D3) Format
SEGMENT’S BIT SETTING
IN PLANE P1
SEGMENT’S BIT SETTING
IN PLANE P0
SEGMENT
BEHAVIOR
0 0 Segment off.
01
Segment on only during the 1st half of each
blink period.
10
Segment on only during the 2nd half of each
blink period.
1 1 Segment on.
Table 21. Digit Register Mapping with Blink Globally Enabled
REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
Blink timing counters are unaffected. P I R 0 E B X S
Blink timing counters are reset during the I2C acknowledge. P I R 1 E B X S
Table 22. Global Blink Timing Synchronization (T Data Bit D4) Format
REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
Digit data for both planes P0 and P1 are unaffected. P I 0 T E B X S
D i g i t d ata for b oth p l anes P 0 and P 1 ar e cl ear ed d ur i ng the I2
C acknow l ed g e.P I 1TEBXS
Table 23. Global Clear Digit Data (R Data Bit D5) Format
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
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REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
Intensity for all digits is controlled by one setting in the global intensity register. P 0 R T E B X S
Intensity for digits is controlled by the individual settings in the intensity10 and
intensity76 registers. P1RTEBXS
Table 24. Global Intensity (I Data Bit D6) Format
REGISTER DATA
MODE D7 D6 D5 D4 D3 D2 D1 D0
P1 Blink Phase 0 I R T E B X S
P0 Blink Phase 1 I R T E B X S
Table 25. Blink Phase Readback (P Data Bit D7) Format
REGISTER DATA
SCAN
LIMIT
ADDRESS CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
HEX
CODE
Display Digit 0 only 0x03 X X X X X 0 0 0 0x00
Display Digits 0 and 1 0x03 X X X X X 0 0 1 0x01
Display Digits 0 1 2 0x03 X X X X X 0 1 0 0x02
Display Digits 0 1 2 3 0x03 X X X X X 0 1 1 0x03
Display Digits 0 1 2 3 4 0x03 X X X X X 1 0 0 0x04
Display Digits 0 1 2 3 4 5 0x03 X X X X X 1 0 1 0x05
Display Digits 0 1 2 3 4 5 6 0x03 X X X X X 1 1 0 0x06
Display Digits 0 1 2 3 4 5 6 7 0x03 X X X X X 1 1 1 0x07
Table 26. Scan-Limit Register Format
REGISTER DATA
DUTY
CYCLE
TYPICAL
SEGMENT
CURRENT (mA)
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
HEX
CODE
1/16 (min on) 2.5 0x02 X X X X 0 0 0 0 0xX0
2/16 5 0x02 X X X X 0 0 0 1 0xX1
3/16 7.5 0x02 X X X X 0 0 1 0 0xX2
4/16 10 0x02 X X X X 0 0 1 1 0xX3
5/16 12.5 0x02 X X X X 0 1 0 0 0xX4
6/16 15 0x02 X X X X 0 1 0 1 0xX5
7/16 17.5 0x02 X X X X 0 1 1 0 0xX6
8/16 20 0x02 X X X X 0 1 1 1 0xX7
9/16 22.5 0x02 X X X X 1 0 0 0 0xX8
10/16 25 0x02 X X X X 1 0 0 1 0xX9
11/16 27.5 0x02 X X X X 1 0 1 0 0xXA
12/16 30 0x02 X X X X 1 0 1 1 0xXB
13/16 32.5 0x02 X X X X 1 1 0 0 0xXC
14/16 35 0x02 X X X X 1 1 0 1 0xXD
15/16 37.5 0x02 X X X X 1 1 1 0 0xXE
15/16 (max on) 37.5 0x02 X X X X 1 1 1 1 0xXF
Table 27. Global Intensity Register Format
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 28www.maximintegrated.com
REGISTER DATA
REGISTER
FUNCTION
ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Intensity10 Register 0x10 Digit 1 Digit 0
Intensity32 Register 0x11 Digit 3 Digit 2
Intensity54 Register 0x12 Digit 5 Digit 4
Intensity76 Register 0x13 Digit 7 Digit 6
Intensity10a Register 0x14 Digit 1a (7 segment only) Digit 0a (7 segment only)
Intensity32a Register 0x15 Digit 3a (7 segment only) Digit 2a (7 segment only)
Intensity54a Register 0x16 Digit 5a (7 segment only) Digit 4a (7 segment only)
Intensity76a Register 0x17 Digit 7a (7 segment only) Digit 6a (7 segment only)
Table 28. Individual Segment Intensity Registers
REGISTER DATA
DUTY
CYCLE
TYPICAL
SEGMENT
CURRENT (mA)
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
HEX
CODE
1/16 (min on) 2.5 0x10 to 0x17 00000xX0
2/16 5 0x10 to 0x17 00010xX1
3/16 7.5 0x10 to 0x17 00100xX2
4/16 10 0x10 to 0x17 00110xX3
5/16 12.5 0x10 to 0x17 01000xX4
6/16 15 0x10 to 0x17 01010xX5
7/16 17.5 0x10 to 0x17 01100xX6
8/16 20 0x10 to 0x17 01110xX7
9/16 22.5 0x10 to 0x17 10000xX8
10/16 25 0x10 to 0x17 10010xX9
11/16 27.5 0x10 to 0x17 10100xXA
12/16 30 0x10 to 0x17 10110xXB
13/16 32.5 0x10 to 0x17 11000xXC
14/16 35 0x10 to 0x17 11010xXD
15/16 37.5 0x10 to 0x17 11100xXE
15/16 (max on) 37.5 0x10 to 0x17
See Table 30.
11110xXF
Table 29. Even Individual Segment Intensity Format
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 29www.maximintegrated.com
REGISTER DATA
DUTY
CYCLE
TYPICAL
SEGMENT
C U R R EN T ( m A )
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
HEX
CODE
1/16 (min on) 2.5 0x10 to 0x17 0 0 0 0 0x0X
2/16 5 0x10 to 0x17 0 0 0 1 0x1X
3/16 7.5 0x10 to 0x17 0 0 1 0 0x2X
4/16 10 0x10 to 0x17 0 0 1 1 0x3X
5/16 12.5 0x10 to 0x17 0 1 0 0 0x4X
6/16 15 0x10 to 0x17 0 1 0 1 0x5X
7/16 17.5 0x10 to 0x17 0 1 1 0 0x6X
8/16 20 0x10 to 0x17 0 1 1 1 0x7X
9/16 22.5 0x10 to 0x17 1 0 0 0 0x8X
10/16 25 0x10 to 0x17 1 0 0 1 0x9X
11/16 27.5 0x10 to 0x17 1 0 1 0 0xAX
12/16 30 0x10 to 0x17 1 0 1 1 0xBX
13/16 32.5 0x10 to 0x17 1 1 0 0 0xCX
14/16 35 0x10 to 0x17 1 1 0 1 0xDX
15/16 37.5 0x10 to 0x17 1 1 1 0 0xEX
15/16 (max on) 37.5 0x10 to 0x17 1 1 1 1
See Table 29
0xFX
Table 30. Odd Individual Segment Intensity Format
REGISTER DATA
MODE ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
Write GPIO Data 0x05 X X X P4 P3 P2 P1 P0
Read GPIO Data 0x05 0 0 0 P4 or IRQ status P3 P2 P1 P0
Table 31. GPIO Data Register
KEYS
SCANNED
PORTS
AVAILABLE P0 P1 P2 P3 P4
None 5 pins GPIO GPIO GPIO GPIO GPIO
1 to 8 3 pins Key_A GPIO GPIO GPIO IRQ
9 to 16 2 pins Key_A Key_B GPIO GPIO IRQ
17 to 24 1 pin Key_A Key_B Key_C GPIO IRQ
25 to 36 None Key_A Key_B Key_C Key_D IRQ
Table 32. Port Scanning Function Allocation
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 30www.maximintegrated.com
REGISTER DATA
MODE ADDRESS
CODE (HEX) D7 D6 D5 D4 D3 D2 D1 D0
GPIO
Configuration
Register
0x06 Set number of keys scanned Set port direction for ports P0 to P4:
0 = output, 1 = input
PORT ALLOCATION OPTIONS
0 Keys Scanned 0x06 0 0 0 P4 P3 P2 P1 P0
8 Keys Scanned 0x06 0 0 1 IRQ P3 P2 P1 Key_A
16 Keys Scanned 0x06 0 1 0 IRQ P3 P2 Key_B Key_A
24 Keys Scanned 0x06 0 1 1 IRQ P3 Key_C Key_B Key_A
32 Keys Scanned 0x06 1 X X IRQ Key_D Key_C Key_B Key_A
EXAMPLE PORT CONFIGURATION SETTINGS
No Keys
Scanned, P4 and
P2 Are Outputs,
Others Are Inputs
0x06 00001011
8 Keys Scanned,
P3 and P1 Are
Outputs, P2 Is an
Input
0x06 0 1 0 X 0 1 0 X
32 Keys
Scanned, No
GPIO Ports
0x06 1 XXXXXXX
Table 33. Port Configuration Register Format
REGISTER DATA
WITH APPROPRIATE SWITCH NAMED BELOW
KEY
MASK
REGISTER
ADDRESS
CODE
(HEX D7 D6 D5 D4 D3 D2 D1 D0
Key_A Mask
Register 0x08 SW_A7 SW_A6 SW_A5 SW_A4 SW_A3 SW_A2 SW_A1 SW_A0
Key_B Mask
Register 0x09 SW_B7 SW_B6 SW_B5 SW_B4 SW_B3 SW_B2 SW_B1 SW_B0
Key_C Mask
Register 0x0A SW_C7 SW_C6 SW_C5 SW_C4 SW_C3 SW_C2 SW_C1 SW_C0
Key_D Mask
Register 0x0B SW_ D7 SW_D6 SW_D5 SW_D4 SW_D3 SW_D2 SW_D1 SW_D0
Table 34. Key Mask Register Format (Write Only)
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 31www.maximintegrated.com
REGISTER DATA
KEY
DEBOUNCED
REGISTER
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Key_A
Debounced
Register
0x08 SW_A7 SW_A6 SW_A5 SW_A4 SW_A3 SW_A2 SW_A1 SW_A0
Key_B
Debounced
Register
0x09 SW_B7 SW_B6 SW_B5 SW_B4 SW_B3 SW_B2 SW_B1 SW_B0
Key_C
Debounced
Register
0x0A SW_C7 SW_C6 SW_C5 SW_C4 SW_C3 SW_C2 SW_C1 SW_C0
Key_D
Debounced
Register
0x0B SW_D7 SW_D6 SW_D5 SW_D4 SW_D3 SW_D2 SW_D1 SW_D0
Table 35. Key Debounced Register Format (Read Only)
REGISTER DATA
KEY
PRESSED
REGISTER
ADDRESS
CODE
(HEX D7 D6 D5 D4 D3 D2 D1 D0
Key_A
Pressed
Register
0x0C SW_A7 SW_A6 SW_A5 SW_A4 SW_A3 SW_A2 SW_A1 SW_A0
Key_B
Pressed
Register
0x0D SW_B7 SW_B6 SW_B5 SW_B4 SW_B3 SW_B2 SW_B1 SW_B0
Key_C
Pressed
Register
0x0E SW_C7 SW_C6 SW_C5 SW_C4 SW_C3 SW_C2 SW_C1 SW_C0
Key_D
Pressed
Register
0x0F SW_D7 SW_D6 SW_D5 SW_D4 SW_D3 SW_D2 SW_D1 SW_D0
Table 36. Key Pressed Register Format (Read Only)
REGISTER DATA
MODE
ADDRESS
CODE
(HEX) D7 D6 D5 D4 D3 D2 D1 D0
Normal Operation 0x07 X XXXXXX0
Display Test 0x07 X XXXXXX1
Table 37. Display Test Register
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 32www.maximintegrated.com
C O N F I G U R A T IO N
C H O IC E
C o m m o n - C a t h o d e
D r i v e : D ig it Ty p e
CC0: 16-seg monocolor
CC1: 16-seg monocolor
CC0 and CC1:
(2) 7-seg bicolor
or (4) 7-seg monocolor
or (1) 7-seg bicolor
and (2) 7-seg monocolor*
CC0 and CC1:
(1)16-seg bicolor
CC0: 16-seg monocolor
CC0: (2) 7-seg monocolor*
or 7-seg bicolor
CC1: 14-seg monocolor
CC0: 14-seg monocolor
CC1: 16-seg monocolor
CC1: (2) 7-seg monocolor*
or 7-seg bicolor
CC0 and CC1: (2) 14-seg
monocolor or 14-seg
bicolor
00 CC0 — CC0 CC0 CC0 CC0 — CC0 — — CC0
01 — CC1 CC1 CC1 — — CC1 — CC1 CC1 CC1
02 a1 a1 1a a1 a1 1a a a a1 1a a
03 a2 a2 — a2 a2 — — — a2 — —
04 bb 1b bb1bbbb1b b
05 cc 1c cc1cccc1c c
06 d1 d1 1d d1 d1 1d d d d1 1d d
07 d2 d2 1dp d2 d2 1dp — — d2 1dp —
08 ee 1e ee1eeee1e e
09 ff 1f ff1ffff1f f
010 g1 g1 1g g1 g1 1g g1 g1 g1 1g g1
011 g2 g2 2a g2 g2 2a g2 g2 g2 2a g2
012 hh 2b hh2bhhh2b h
013 ii 2c ii2ciii2c i
014 jj 2d jj2djjj2d k
015 kk 2e kk2ekkk2e l
016 ll 2f ll2flll2f l
017 mm 2g mm2gmmm2g m
018 dp dp 2dp dp dp 2dp dp dp dp 2dp dp
ADDRESS
CODE (HEX) 0x0C
D7
D6 See Table 41.
D5
D4 See Table 40.
D3
D2 See Table 39.
D1 0101
REGISTER DATA
D0 0 0 1 1
Table 38. Slot 1 Configuration
*
7-segment digits can be replaced by directly controlled discrete LEDs according to settings in decode mode register (Table 11).
**
The highlighted row is used in Typical Operating Circuit 1 for display digits 0 and 1.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 33www.maximintegrated.com
*
7-segment digits can be replaced by directly controlled discrete LEDs according to settings in decode mode register (Table 11).
**
The highlighted row is used in Typical Operating Circuit 1 for display digits 2 and 3.
C O N F I G U R A T IO N
C H O IC E
C o m m o n - C a t h o d e
D r i v e : D ig it Ty p e
CC2: 16-seg monocolor
CC3: 16-seg monocolor
CC2 and CC3:
(2) 7-seg bicolor
or (4) 7-seg monocolor
or (1) 7-seg bicolor
and (2) 7-seg monocolor*
CC2 and CC3:
(1)16-seg bicolor
CC2: 16-seg monocolor
CC2: (2) 7-seg monocolor*
or 7-seg bicolor
CC3: 14-seg monocolor
CC2: 14-seg monocolor
CC3: 16-seg monocolor
CC3: (2) 7-seg monocolor*
or 7-seg bicolor
CC2 and CC3: (2) 14-seg
monocolor or 14-seg
bicolor
00 a1 a1 1a a1 a1 1a a a a1 1a a
01 a2 a2 — a2 a2 — — — a2 — —
02 CC2 — CC2 CC2 CC2 CC2 — CC2 — — CC2
03 — CC3 CC3 CC3 — — CC3 — CC3 CC3 CC3
04 b b 1b b b 1b b b b 1b b
05 c c 1c c c 1c c c c 1c c
06 d1 d1 1d d1 d1 1d d d d1 1d d
07 d2 d2 1dp d2 d2 1dp — — d2 1dp —
08 e e 1e e e 1e e e e 1e e
09 f f 1f f f 1f f f f 1f f
010 g1 g1 1g g1 g1 1g g1 g1 g1 1g g1
011 g2 g2 2a g2 g2 2a g2 g2 g2 2a g2
012 h h 2b h h 2b h h h 2b h
013 i i 2c i i 2c i i i 2c i
014 j j 2d j j 2d j j j 2d k
015 k k 2e k k 2e k k k 2e l
016 l l 2f l l 2f l l l 2f l
017 m m 2g m m 2g m m m 2g m
018 dp dp 2dp dp dp 2dp dp dp dp 2dp dp
ADDRESS
CODE (HEX) 0x0C
D7
D6 See Table 41.
D5
D4 See Table 40.
D3 0101
D2 0 0 1 1
D1
REGISTER DATA
D0 See Table 38.
Table 39. Slot 2 Configuration
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 34www.maximintegrated.com
C O N F I G U R A T IO N
C H O IC E
C o m m o n - C a t h o d e
D r i v e : D ig it Ty p e
CC4: 16-seg monocolor
CC5: 16-seg monocolor
CC4 and CC5:
(2) 7-seg bicolor
or (4) 7-seg monocolor
or (1) 7-seg bicolor
and (2) 7-seg monocolor*
CC4 and CC5:
(1)16-seg bicolor
CC4: 16-seg monocolor
CC4: (2) 7-seg monocolor*
or 7-seg bicolor
CC5: 14-seg monocolor
CC4: 14-seg monocolor
CC5: 16-seg monocolor
CC5: (2) 7-seg monocolor*
or 7-seg bicolor
CC4 and CC5: (2) 14-seg
monocolor or 14-seg
bicolor
00 a1 a1 1a a1 a1 1a a a a1 1a a
01 a2 a2 —a2a2———a2——
02 b b 1b b b 1b b b b 1b b
03 c c 1c c c 1c c c c 1c c
04 CC4 —CC4 CC4 CC4 CC4 — CC4 — — CC4
05 —CC5 CC5 CC5 — — CC5 — CC5 CC5 CC5
06 d1 d1 1d d1 d1 1d d d d1 1d d
07 d2 d2 1dp d2 d2 1dp — — d2 1dp —
08 e e 1e e e 1e e e e 1e e
09 f f 1f f f 1f f f f 1f f
010 g1 g1 1g g1 g1 1g g1 g1 g1 1g g1
011 g2 g2 2a g2 g2 2a g2 g2 g2 2a g2
012 h h 2b h h 2b h h h 2b h
013 i i 2c i i 2c i i i 2c i
014 j j 2d j j 2d j j j 2d k
015 k k 2e k k 2e k k k 2e l
016 l l 2f l l 2f l l l 2f l
017 m m 2g m m 2g m m m 2g m
018 dp dp 2dp dp dp 2dp dp dp dp 2dp dp
ADDRESS
CODE (HEX) 0x0C
D7
D6 See Table 41.
D5 0101
D4 0 0 1 1
D3
D2 See Table 39.
D1
REGISTER DATA
D0 See Table 38.
Table 40. Slot 3 Configuration
*
7-segment digits can be replaced by directly controlled discrete LEDs according to settings in decode mode register (Table 11).
**
The highlighted row is used in Typical Operating Circuit 1 for display digits 4 and 5.
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 35www.maximintegrated.com
*
7-segment digits can be replaced by directly controlled discrete LEDs according to settings in the decode mode register (Table 11).
**
The highlighted row is used in Typical Operating Circuit 1 for display digits 6 and 7.
C O N F I G U R A T IO N
C H O IC E
C o m m o n - C a t h o d e
D r i v e : D ig it Ty p e
CC6: 16-seg monocolor
CC7: 16-seg monocolor
CC6 and CC7:
(2) 7-seg bicolor
or (4) 7-seg monocolor
or (1) 7-seg bicolor
and (2) 7-seg monocolor*
CC6 and CC7:
(1)16-seg bicolor
CC6: 16-seg monocolor
CC6: (2) 7-seg monocolor*
or 7-seg bicolor
CC7: 14-seg monocolor
CC6: 14-seg monocolor
CC7: 16-seg monocolor
CC7: (2) 7-seg monocolor*
or 7-seg bicolor
CC6 and CC7: (2) 14-seg
monocolor or 14-seg
bicolor
00 a1 a1 1a a1 a1 1a a a a1 1a a
01 a2 a2 — a2 a2 — — — a2 — —
02 bb 1b bb1bbbb1b b
03 cc 1c cc1cccc1c c
04 d1 d1 1d d1 d1 1d d d d1 1d d
05 d2 d2 1dp d2 d2 1dp — — d2 1dp —
06 CC6 — CC6 CC6 CC6 CC6 — CC6 — — CC6
07 — CC7 CC7 CC7 — — CC7 — CC7 CC7 CC7
08 ee 1e ee1eeee1e e
09 ff 1f ff1ffff1f f
010 g1 g1 1g g1 g1 1g g1 g1 g1 1g g1
011 g2 g2 2a g2 g2 2a g2 g2 g2 2a g2
012 hh 2b hh2bhhh2b h
013 ii 2c ii2ciii2c i
014 jj 2d jj2djjj2d k
015 kk 2e kk2ekkk2e l
016 ll 2f ll2flll2f l
017 mm 2g mm2gmmm2g m
018 dp dp 2dp dp dp 2dp dp dp dp 2dp dp
ADDRESS
CODE (HEX) 0x0C
D7 0101
D6 0 0 1 1
D5
D4 See Table 40.
D3
D2 See Table 39.
D1
REGISTER DATA
D0 See Table 38.
Table 41. Slot 4 Configuration
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 36www.maximintegrated.com
f
a
Rcc
dp
g
Gcc
b
c
e
d
DIGIT 0b (RED), DIGIT 1b (GREEN)
7-SEGMENT BICOLOR LED
O16
O17
O18
O0
O1
O11
O12
O13
O14
O0
O2
O3
O4
O15
f
a
h
g2
g1
i
b
c
e
d
DIGITS 2 AND 3
14-SEGMENT BICOLOR
DIGIT 6
4 x 4 MATRIX OF DISCRETE MONOCOLOR LEDs
O8
O9
O10
O11
O12
O0
O4
O5
O6
m
Rcc
dp
Ccc
j
l
k
O16
O17
O18
O2
O3
O13
O14
O15
f
a
CC1
dp
g
CC0
b
c
e
d
DIGITS 0a AND 1a
7-SEGMENT MONOCOLOR
O9
O10
O7
O1
O0
O2
O4
O5
O6
O8
d2
a1
g1
f
e
g2
a2
b
d1
c
DIGIT 5
16-SEGMENT MONOCOLOR
O6
O7
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O5
O11
O12
O13
d2
a1
g1
f
e
g2
a2
b
d1
c
DIGIT 4
16-SEGMENT MONOCOLOR
O6
O7
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O4
O11
O12
O13
3.3V
100nF
47µF
O0
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
P0
P1
P2
P3
P4/IRQ
ISET
RSET
OSC_OUT
OSC
V+
V+
GND
GND
AD1
V+
GND
AD0
SCL
SDA
BLINK
O5
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
O6
CSET
O0
O2
O3
O4
DIGIT 7
4 x 4 MATRIX OF DISCRETE MONOCOLOR LEDs
O5
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
O7
MAX6955
Typical Operating Circuits
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 37www.maximintegrated.com
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 0
O6
O7
O8
O9
O10
O2
O3
O4
O5
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O0
O11
O12
O13
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 2
O6
O7
O8
O9
O10
O0
O1
O4
O5
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O2
O11
O12
O13
3.3V
100nF
47µF
O0
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
P0
P1
P2
P3
P4/IRQ
ISET
RSET
OSC_OUT
OSC
V+
V+
GND
GND
V+
GND
BLINK
CSET
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 1
O6
O7
O8
O9
O10
O2
O3
O4
O5
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O1
O11
O12
O13
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 3
O6
O7
O8
O9
O10
O0
O1
O4
O5
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O3
O11
O12
O13
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 6
O4
O5
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O6
O11
O12
O13
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 7
O4
O5
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O7
O11
O12
O13
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 4
O6
O6
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O4
O11
O12
O13
d2
a
g1
f
e
g2
a2
b
d1
c
DIGIT 5
O6
O7
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O5
O11
O12
O13
MAX6955
AD1
AD0
SCL
SDA
AD1
AD0
SCL
SDA
Typical Operating Circuits (continued)
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 38www.maximintegrated.com
f
a
Rcc
dp
g
Gcc
b
c
e
d
DIGIT 0b (RED), DIGIT 1b (GREEN)
7-SEGMENT BICOLOR LED
O16
O17
O18
O0
O1
O11
O12
O13
O14
O0
O1
O2
O3
O15
f
a
h
g2
g1
i
b
c
e
d
DIGITS 2 AND 3
14-SEGMENT BICOLOR
DIGIT 6
4 x 4 MATRIX OF DISCRETE MONOCOLOR LEDs
O8
O9
O10
O11
O12
O0
O4
O5
O6
m
Rcc
dp
Ccc
j
l
k
O16
O17
O18
O2
O3
O13
O14
O15
f
a
CC1
dp
g
CC0
b
c
e
d
DIGITS 0a AND 1a
7-SEGMENT MONOCOLOR
O9
O10
O7
O1
O0
O2
O4
O5
O6
O8
d2
a1
g1
f
e
g2
a2
b
d1
c
DIGIT 5
16-SEGMENT MONOCOLOR
O6
O7
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O5
O11
O12
O13
d2
a1
g1
f
e
g2
a2
b
d1
c
DIGIT 4
16-SEGMENT MONOCOLOR
O6
O7
O8
O9
O10
O0
O1
O2
O3
k
m
l
dp
h
j
i
O14
O15
O16
O17
O18
cc
O4
O11
O12
O13
3.3V
100nF
47µF
O0
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
P0
P1
P2
P3
P4/IRQ
ISET
RSET
OSC_OUT
OSC
V+
V+
GND
GND
AD1
V+
GND
AD0
SCL
SDA
BLINK
O4
O5
O6
O7
O0
O1
O2
O3
O4
O5
O6
O7
P1
CSET
O0
O1
O2
O3
DIGIT 7
4 x 4 MATRIX OF DISCRETE MONOCOLOR LEDs
O4
O5
O6
O7
O0
O1
O2
O3
O4
O5
O6
O7
P3
MAX6955
SW00
SW01
SW02
SW03
SW04
SW05
SW06
SW07
SW10
SW11
SW12
SW13
SW14
SW15
SW16
SW17
P0 P2
SW20
SW21
SW22
SW23
SW24
SW25
SW26
SW27
SW30
SW31
SW32
SW33
SW34
SW35
SW36
SW37
Typical Operating Circuits (continued)
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated | 39www.maximintegrated.com
TOP VIEW
SSOP
MAX6955
1
2
3
4
5
6
7
8
9
10
11
12
13
14
O7
O6
O5
O4
O3
O2
O1
O0
AD1
SCL
SDA
AD0
P1
P0
15
16
17
18GND
ISET
GND
O8
36
35
34
33
32
31
30
29
28
27
26
25
24
23
P4/IRQ
P3
P2
OSC_OUT
BLINK
O18
O10
O17
O16
O15
O14
O13
O12
O11
22
21
20
19 V+
O9
OSC
V+
O18
O17
O15
O14
O11
O10
O9
EP*
O13
O12
O16
O1
O2
O3
O4
O5
O6
O7
O8
O0
AD1 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
GND
V+
OSC
V+
N.C.
ISET
GND
GND
N.C.
SDA
AD0
P1
P0
P4/IRQ
P3
P2
OSC_OUT
BLINK
SCL
TQFN-EP
+
MAX6955
V+
*EP = EXPOSED PAD. CONNECT EP TO GND.
Pin Configurations
Chip Information
PROCESS: CMOS
Package Information
For the latest package outline information and land patterns (foot-
prints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
36 SSOP A36-2 21-0040 90-0098
40 TQFN-EP T4066+5 21-0141 90-0055
MAX6955 2-Wire Interfaced, 2.7V to 5.5V
LED Display Driver with I/O
Expander and Key Scan
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2015 Maxim Integrated Products, Inc. | 40
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Revision History
REVISION
NUMBER
REVISION
DATE
DESCRIPTION
PAGES
CHANGED
0 — Initial release —
1 — — —
2 12/06 — —
3 3/08 Corrected data sheet errors. 1, 2, 3, 6, 15, 16,
18, 19, 36, 37, 38
4 7/15
Removed automotive reference from data sheet and updated Benefits and
Features section 1
Mouser Electronics
Authorized Distributor
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