M
1998 Microchip Technology Inc.
Preliminary
DS30453B-page 1
PIC16C5X
Devices Included in this Data Sheet:
PIC16C52
PIC16C54s
PIC16CR54s
PIC16C55s
PIC16C56s
PIC16CR56s
PIC16C57s
PIC16CR57s
PIC16C58s
PIC16CR58s
High-Performance RISC CPU:
Only 33 single word instructions to learn
All instructions are single cycle (200 ns) except f or
program branches which are two-cycle
Operating speed: DC - 20 MHz clock input
DC - 200 ns instruction cycle
Note: The letter "s" used following the part
numbers throughout this document
indicate plural, meaning there is more
than one part variety for the indicated
device.
Device Pins I/O EPROM/
ROM RAM
PIC16C52 18 12 384 25
PIC16C54 18 12 512 25
PIC16C54A 18 12 512 25
PIC16C54B 18 12 512 25
PIC16C54C 18 12 512 25
PIC16CR54A 18 12 512 25
PIC16CR54B 18 12 512 25
PIC16CR54C 18 12 512 25
PIC16C55 28 20 512 24
PIC16C55A 28 20 512 24
PIC16C56 18 12 1K 25
PIC16C56A 18 12 1K 25
PIC16CR56A 18 12 1K 25
PIC16C57 28 20 2K 72
PIC16C57C 28 20 2K 72
PIC16CR57B 28 20 2K 72
PIC16CR57C 28 20 2K 72
PIC16C58A 18 12 2K 73
PIC16C58B 18 12 2K 73
PIC16CR58A 18 12 2K 73
PIC16CR58B 18 12 2K 73
12-bit wide instructions
8-bit wide data path
Seven or eight special function hardware registers
Two-level deep hardware stack
Direct, indirect and relative addressing modes for
data and instructions
Peripheral Features:
8-bit real time clock/counter (TMR0) with 8-bit
programmable prescaler
Power-On Reset (POR)
Device Reset Timer (DRT)
Watchdog Timer (WDT) with its own on-chip
RC oscillator for reliable operation
Programmable code-protection
Power saving SLEEP mode
Selectable oscillator options:
- RC: Low-cost RC oscillator
- XT: Standard crystal/resonator
- HS: High-speed crystal/resonator
- LP: Power saving, low-frequency crystal
CMOS Technology:
Low-power, high-speed CMOS EPROM/ROM
technology
Fully static design
Wide-operating voltage and temperature range:
- EPROM Commercial/Industrial 2.0V to 6.25V
- ROM Commercial/Industrial 2.0V to 6.25V
- EPROM Extended 2.5V to 6.0V
- ROM Extended 2.5V to 6.0V
Low-power consumption
- < 2 mA typical @ 5V, 4 MHz
- 15
µ
A typical @ 3V, 32 kHz
- < 0.6
µ
A typical standby current
(with WDT disabled) @ 3V, 0
°
C to 70
°
C
Note: In this document, figure and table titles
refer to all varieties of the part number
indicated, (i.e., The title "Figure 14-1:
Load Conditions - PIC16C54A", also
refers to PIC16LC54A and PIC16LV54A
parts).
EPROM/ROM-Based 8-Bit CMOS Microcontroller Series
PIC16C5X
DS30453B-page 2
Preliminary
1998 Microchip Technology Inc.
Pin Diagrams
PDIP, SOIC, Windowed CERDIP
PIC16CR54s
PIC16C58s
PIC16CR58s
PIC16C54s
RA1
RA0
OSC1/CLKIN
OSC2/CLKOUT
VDD
VDD
RB7
RB6
RB5
RB4
RA2
RA3
T0CKI
MCLR/VPP
VSS
VSS
RB0
RB1
RB2
RB3
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
SSOP
PIC16C56s
PIC16CR56s
PIC16CR54s
PIC16C58s
PIC16CR58s
PIC16C54s
PIC16C56s
PIC16CR56s
RA2
RA3
T0CKI
MCLR/VPP
VSS
RB0
RB1
RB2
RB3
1
2
3
4
5
6
7
8
910
18
17
16
15
14
13
12
11
RA1
RA0
OSC1/CLKIN
OSC2/CLKOUT
VDD
RB7
RB6
RB5
RB4
PIC16C52s
28
27
26
25
24
23
22
21
20
19
18
17
16
15
•1
2
3
4
5
6
7
8
9
10
11
12
13
14
PDIP, SOIC, Windowed CERDIP
PIC16C57s
PIC16C55s
MCLR/VPP
OSC1/CLKIN
OSC2/CLKOUT
RC7
RC6
RC5
RC4
RC3
RC2
RC1
RC0
RB7
RB6
RB5
T0CKI
VDD
VSS
RA0
RA1
RA2
RA3
RB0
RB1
RB2
RB3
RB4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
PIC16C57s
SSOP
PIC16C55s
VDD
VSS
PIC16CR57s
PIC16CR57s
T0CKI
VDD
N/C
VSS
N/C
RA0
RA1
RA2
RA3
RB0
RB1
RB2
RB3
RB4
MCLR/VPP
OSC1/CLKIN
OSC2/CLKOUT
RC7
RC6
RC5
RC4
RC3
RC2
RC1
RC0
RB7
RB6
RB5
1998 Microchip Technology Inc.
Preliminary
DS30453B-page 3
PIC16C5X
Device Differences
Note 1:
If you change from this device to another device, please verify oscillator characteristics in your application.
Note 2:
In PIC16LV58A, MCLR Filter = Yes
Device Voltage
Range
Oscillator
Selection
(Program) Oscillator Process
Technology
(Microns)
ROM
Equivalent MCLR
Filter
PIC16C52 3.0-6.25 User See Note 1 0.9 No
PIC16C54 2.5-6.25 Factory See Note 1 1.2 PIC16CR54A No
PIC16C54A 2.0-6.25 User See Note 1 0.9 No
PIC16C54B 2.5-5.5 User See Note 1 0.7 PIC16CR54B Yes
PIC16C54C 2.5-5.5 User See Note 1 0.7 PIC16CR54C Yes
PIC16C55 2.5-6.25 Factory See Note 1 1.7 No
PIC16C55A 2.5-5.5 User See Note 1 0.7 Yes
PIC16C56 2.5-6.25 Factory See Note 1 1.7 No
PIC16C56A 2.5-5.5 User See Note 1 0.7 PIC16CR56A Yes
PIC16C57 2.5-6.25 Factory See Note 1 1.2 No
PIC16C57C 2.5-5.5 User See Note 1 0.7 PIC16CR57C Yes
PIC16C58A 2.0-6.25 User See Note 1 0.9 PIC16CR58A No
(2)
PIC16C58B 2.5-5.5 User See Note 1 0.7 PIC16CR58B Yes
PIC16CR54A 2.5-6.25 Factory See Note 1 1.2 N/A Yes
PIC16CR54B 2.5-5.5 Factory See Note 1 0.7 N/A Yes
PIC16CR54C 2.5-5.5 Factory See Note 1 0.7 N/A Yes
PIC16CR56A 2.5-5.5 Factory See Note 1 0.7 N/A Yes
PIC16CR57B 2.5-6.25 Factory See Note 1 0.9 N/A Yes
PIC16CR57C 2.5-5.5 Factory See Note 1 0.7 N/A Yes
PIC16CR58A 2.5-6.25 Factory See Note 1 0.9 N/A Yes
PIC16CR58B 2.5-5.5 Factory See Note 1 0.7 N/A Yes
PIC16C5X
DS30453B-page 4
Preliminary
1998 Microchip Technology Inc.
Table of Contents
1.0 General Description.............................................................................................................................................5
2.0 PIC16C5X Device Varieties.................................................................................................................................7
3.0 Architectural Overview.........................................................................................................................................9
4.0 Memory Organization ........................................................................................................................................15
5.0 I/O Ports.............................................................................................................................................................25
6.0 Timer0 Module and TMR0 Register...................................................................................................................27
7.0 Special Features of the CPU.............................................................................................................................31
8.0 Instruction Set Summary ...................................................................................................................................43
9.0 Development Support........................................................................................................................................55
10.0 Electrical Characteristics - PIC16C52................................................................................................................59
11.0 Electrical Characteristics - PIC16C54/55/56/57.................................................................................................67
12.0 DC and AC Characteristics - PIC16C54/55/56/57.............................................................................................81
13.0 Electrical Characteristics - PIC16CR54A...........................................................................................................89
14.0 Electrical Characteristics - PIC16C54A...........................................................................................................103
15.0 Electrical Characteristics - PIC16CR57B.........................................................................................................117
16.0 Electrical Characteristics - PIC16C58A...........................................................................................................131
17.0 Electrical Characteristics - PIC16CR58A.........................................................................................................145
18.0 DC and AC Characteristics - PIC16C54A/CR57B/C58A/CR58A ....................................................................159
19.0 Electrical Characteristics -
PIC16C54B/C54C/CR54B/CR54C/C55A/C56A/CR56A/C57C/CR57C/C58B/CR58B....................................171
20.0 DC and AC Characteristics -
PIC16C54B/C54C/CR54B/CR54C/C55A/C56A/CR56A/C57C/CR57C/C58B/CR58B....................................183
21.0 Packaging Information.....................................................................................................................................195
Appendix A: Compatibility ...........................................................................................................................................207
Index .........................................................................................................................................................................209
On-Line Support..........................................................................................................................................................211
PIC16C5X Product Identification System....................................................................................................................213
PIC16C54/55/56/57 Product Identification System.....................................................................................................214
To Our Valued Customers
Most Current Data Sheet
To obtain the most up-to-date version of this data sheet, please check our Worldwide Web site at:
http://www.microchip.com
You can determine the version of a data sheet by examining its literature number found on the bottom outside corner of any page.
The last character of the literature number is the version number. e.g., DS30000A is version A of document DS30000.
Errata
An errata sheet may exist for current devices, describing minor operational differences (from the data sheet) and recommended
workarounds. As de vice/documentation issues become known to us , we will pub lish an errata sheet. The errata will specify the revi-
sion of silicon and revision of document to which it applies.
To determine if an errata sheet exists for a particular device, please check with one of the following:
Microchip’ s W orldwide Web site; http://www .microchip .com
Your local Microchip sales office (see last page)
The Microchip Corporate Literature Center; U.S. FAX: (602) 786-7277
When contacting a sales office or the literature center, please specify which device, revision of silicon and data sheet (include lit-
erature number) you are using.
Corrections to this Data Sheet
We constantly strive to improve the quality of all our products and documentation. We have spent a great deal of time to ensure
that this document is correct. Howev er, we realize that we may have missed a f e w things . If you find any information that is missing
or appears in error, please:
Fill out and mail in the reader response form in the back of this data sheet.
E-mail us at webmaster@microchip.com.
We appreciate your assistance in making this a better document.
1998 Microchip Technology Inc.
Preliminary
DS30453B-page 5
PIC16C5X
1.0 GENERAL DESCRIPTION
The PIC16C5X from Microchip Technology is a family
of low-cost, high performance, 8-bit, fully static,
EPROM/ ROM-based CMOS microcontrollers. It
employs a RISC architecture with only 33 single
word/single cycle instructions. All instructions are sin-
gle cycle (200 ns) except for program branches which
take two cycles. The PIC16C5X delivers perfor mance
an order of magnitude higher than its competitors in the
same price category. The 12-bit wide instructions are
highly symmetrical resulting in 2:1 code compression
over other 8-bit microcontrollers in its class. The easy
to use and easy to remember instruction set reduces
development time significantly.
The PIC16C5X products are equipped with special fea-
tures that reduce system cost and power requirements .
The Power-On Reset (POR) and Device Reset Timer
(DRT) eliminate the need for external reset circuitry.
There are four oscillator configur ations to choose from,
including the power-saving LP (Low Power) oscillator
and cost saving RC oscillator. Power saving SLEEP
mode, Watchdog Timer and code protection features
improve system cost, power and reliability.
The UV erasable CERDIP pac kaged v ersions are ideal
for code development, while the cost-effective One
Time Programmable (OTP) versions are suitable for
production in any volume. The customer can take full
advantage of Microchip’s price leadership in OTP
microcontrollers while benefiting from the OTP’s
flexibility.
The PIC16C5X products are supported by a
full-featured macro assemb ler , a softw are simulator , an
in-circuit emulator, a ‘C’ compiler, fuzzy logic support
tools, a low-cost development programmer, and a full
featured programmer. All the tools are supported on
IBM
PC and compatible machines.
1.1 Applications
The PIC16C5X series fits perfectly in applications rang-
ing from high-speed automotive and appliance motor
control to low-power remote transmitters/receivers,
pointing devices and telecom processors . The EPR OM
technology makes customizing application programs
(transmitter codes, motor speeds, receiver frequen-
cies, etc.) extremely fast and convenient. The small
footprint packages, for through hole or surface mount-
ing, make this microcontroller series perf ect for applica-
tions with space limitations. Low-cost, low-power, high
performance, ease of use and I/O flexibility make the
PIC16C5X series very versatile e ven in areas where no
microcontroller use has been considered before (e.g.,
timer functions, replacement of “glue” logic in larger
systems, coprocessor applications).
PIC16C5X
DS30453B-page 6
Preliminary
1998 Microchip Technology Inc.
TABLE 1-1: PIC16C5X FAMILY OF DEVICES
PIC16C52 PIC16C54s PIC16CR54s PIC16C55s PIC16C56s
Clock
Maximum Frequency
of Operation (MHz) 42020 2020
Memory
EPROM Program Memory
(x12 words) 384 512 512 1K
ROM Program Memory
(x12 words) 512
RAM Data Memory (bytes) 25 25 25 24 25
Peripherals
Timer Module(s) TMR0 TMR0 TMR0 TMR0 TMR0
Features
I/O Pins 12 12 12 20 12
Number of Instructions 33 33 33 33 33
Packages 18-pin DIP,
SOIC 18-pin DIP,
SOIC;
20-pin SSOP
18-pin DIP,
SOIC;
20-pin SSOP
28-pin DIP,
SOIC;
28-pin SSOP
18-pin DIP,
SOIC;
20-pin SSOP
All PICmicro™ F amily devices have Power-on Reset, selectab le Watchdog Timer (except PIC16C52), selectab le code
protect and high I/O current capability.
PIC16CR56s PIC16C57s PIC16CR57s PIC16C58s PIC16CR58s
Clock
Maximum Frequency
of Operation (MHz) 20 20 20 20 20
Memory
EPROM Program Memory
(x12 words) 2K 2K
ROM Program Memory
(x12 words) 1K 2K 2K
RAM Data Memory (bytes) 25 72 72 73 73
Peripherals
Timer Module(s) TMR0 TMR0 TMR0 TMR0 TMR0
Features
I/O Pins 12 20 20 12 12
Number of Instructions 33 33 33 33 33
Packages 18-pin DIP,
SOIC;
20-pin SSOP
28-pin DIP,
SOIC;
28-pin SSOP
28-pin DIP,
SOIC;
28-pin SSOP
18-pin DIP,
SOIC;
20-pin SSOP
18-pin DIP,
SOIC;
20-pin SSOP
All PICmicro™ F amily devices have Power-on Reset, selectab le Watchdog Timer (except PIC16C52), selectab le code
protect and high I/O current capability.
1998 Microchip Technology Inc.
Preliminary
DS30453B-page 7
PIC16C5X
2.0 PIC16C5X DEVICE VARIETIES
A variety of frequency ranges and packaging options
are available. Depending on application and
production requirements, the proper device option can
be selected using the information in this section. When
placing orders, please use the PIC16C5X Product
Identification System at the back of this data sheet to
specify the correct part number.
For the PIC16C5X family of devices, there are four
device types, as indicated in the device number:
1.
C
, as in PIC16C54. These devices have
EPROM program memory and operate over the
standard voltage range.
2.
LC
, as in PIC16LC54A. These devices have
EPROM program memory and operate over an
extended voltage range.
3.
LV
, as in PIC16LV54A. These devices have
EPROM program memory and operate over a
2.0V to 3.8V range.
4.
CR
, as in PIC16CR54A. These devices have
ROM program memory and operate over the
standard voltage range.
5.
LCR
, as in PIC16LCR54B. These devices have
ROM program memory and operate over an
extended voltage range.
2.1 UV Erasable Devices (EPROM)
The UV erasable versions, offered in CERDIP
packages, are optimal for prototype development and
pilot programs
UV erasable devices can be programmed for any of
the four oscillator configurations. Microchip's
PICSTART
and PRO MATE
programmers both
support programming of the PIC16C5X. Third party
programmers also are available; refer to the Third
Party Guide for a list of sources.
2.2 One-Time-Programmable (OTP)
Devices
The availability of OTP devices is especially useful for
customers expecting frequent code changes and
updates.
The OTP devices, packaged in plastic packages,
permit the user to program them once. In addition to
the program memory, the configuration bits must be
programmed.
2.3 Quick-Turnaround-Production (QTP)
Devices
Microchip offers a QTP Programming Service for
factory production orders. This service is made
available for users who choose not to program a
medium to high quantity of units and whose code
patterns have stabilized. The devices are identical to
the OTP devices but with all EPROM locations and
configuration bit options already programmed by the
factory. Certain code and prototype verification
procedures apply before production shipments are
available. Please contact your Microchip Technology
sales office for more details.
2.4 Serialized
Quick-Turnaround-Production
(SQTP ) Devices
Microchip offers the unique programming service
where a few user-defined locations in each device are
programmed with different serial numbers. The serial
numbers may be random, pseudo-random or
sequential. The devices are identical to the OTP
devices but with all EPROM locations and
configuration bit options already programmed by the
factory.
Serial programming allows each device to have a
unique number which can serve as an entry code,
password or ID number.
2.5 Read Only Memory (ROM) Devices
Microchip offers masked ROM versions of several of
the highest volume parts, giving the customer a low
cost option for high volume, mature products.
SM
PIC16C5X
DS30453B-page 8
Preliminary
1998 Microchip Technology Inc.
NOTES:
1998 Microchip Technology Inc.
Preliminary
DS30453B-page 9
PIC16C5X
3.0 ARCHITECTURAL OVERVIEW
The high performance of the PIC16C5X family can be
attributed to a number of architectural features
commonly found in RISC microprocessors. To begin
with, the PIC16C5X uses a Harvard architecture in
which program and data are accessed on separate
buses. This improves bandwidth over traditional von
Neumann architecture where program and data are
fetched on the same bus. Separating program and
data memory further allows instructions to be sized
differently than the 8-bit wide data word. Instruction
opcodes are 12-bits wide making it possible to ha ve all
single word instructions. A 12-bit wide program
memory access bus fetches a 12-bit instruction in a
single cycle. A two-stage pipeline overlaps fetch and
execution of instructions . Consequently, all instructions
(33) execute in a single cycle (200ns @ 20MHz)
except for program branches.
The PIC16C52 addresses 384 x 12 of program
memory, the PIC16C54s/CR54s and PIC16C55s
address 512 x 12 of program memory, the
PIC16C56s/CR56s address 1K X 12 of program
memory, and the PIC16C57s/CR57s and
PIC16C58s/CR58s address 2K x 12 of program
memory. All program memory is internal.
The PIC16C5X can directly or indirectly address its
register files and data memory. All special function
registers including the program counter are mapped in
the data memory. The PIC16C5X has a highly
orthogonal (symmetrical) instruction set that makes it
possible to carry out any operation on any register
using any addressing mode. This symmetrical nature
and lack of ‘special optimal situations’ make
programming with the PIC16C5X simple yet efficient.
In addition, the learning curve is reduced significantly.
The PIC16C5X device contains an 8-bit ALU and
working register. The ALU is a general purpose
arithmetic unit. It performs arithmetic and Boolean
functions between data in the working register and any
register file.
The ALU is 8-bits wide and capable of addition,
subtraction, shift and logical operations. Unless
otherwise mentioned, arithmetic operations are two's
complement in nature. In two-operand instructions,
typically one operand is the W (working) register. The
other operand is either a file register or an immediate
constant. In single operand instructions, the operand
is either the W register or a file register.
The W register is an 8-bit working register used for
ALU operations. It is not an addressable register.
Depending on the instruction executed, the ALU may
affect the values of the Carry (C), Digit Carry (DC),
and Zero (Z) bits in the STATUS register. The C and
DC bits operate as a borrow and digit borrow out bit,
respectively, in subtraction. See the
SUBWF
and
ADDWF
instructions for examples.
A simplified block diagram is shown in Figure 3-1, with
the corresponding device pins described in Table 3-1.
PIC16C5X
DS30453B-page 10
Preliminary
1998 Microchip Technology Inc.
FIGURE 3-1: PIC16C5X SERIES BLOCK DIAGRAM
WDT TIME
OUT
8
STACK 1
ST ACK 2
EPROM/ROM
384 X 12 TO
2048 X 12
INSTRUCTION
REGISTER
INSTRUCTION
DECODER
WATCHDOG
TIMER
CONFIGURATION WORD
OSCILLATOR/
TIMING &
CONTROL
GENERAL
PURPOSE
REGISTER
FILE
(SRAM)
24, 25, 72 or
73 Bytes
WDT/TMR0
PRESCALER
OPTION REG. “OPTION”
“SLEEP”
“CODE
PROTECT”
“OSC
SELECT”
DIRECT ADDRESS
TMR0
FROM W
FROM W
“TRIS 5” “TRIS 6” “TRIS 7”
FSR
TRISA PORTA TRISB PORTC
TRISC
PORTB
FROM W
T0CKI
PIN
9-11
9-11
12
12
8
W
44
4
DATA BUS
8
88
8
8
8
8
ALU
STATUS
FROM W
CLKOUT
8
9
6
5
5-7
OSC1 OSC2 MCLR
LITERALS
PC “DISABLE”
2
RA3:RA0 RB7:RB0 RC7:RC0
(28-Pin
Devices Only)
DIRECT RAM
ADDRESS
1998 Microchip Technology Inc.
Preliminary
DS30453B-page 11
PIC16C5X
TABLE 3-1: PINOUT DESCRIPTION - PIC16C52, PIC16C54s, PIC16CR54s, PIC16C56s,
PIC16CR56s, PIC16C58s, PIC16CR58s
Name DIP, SOIC
No. SSOP
No. I/O/P
Type Input
Levels Description
RA0
RA1
RA2
RA3
17
18
1
2
19
20
1
2
I/O
I/O
I/O
I/O
TTL
TTL
TTL
TTL
Bi-directional I/O port
RB0
RB1
RB2
RB3
RB4
RB5
RB6
RB7
6
7
8
9
10
11
12
13
7
8
9
10
11
12
13
14
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
TTL
TTL
TTL
TTL
TTL
TTL
TTL
TTL
Bi-directional I/O port
T0CKI 3 3 I ST Clock input to Timer0. Must be tied to V
SS
or V
DD,
if not in
use, to reduce current consumption.
MCLR/V
PP
4 4 I ST Master clear (reset) input/programming voltage input. This
pin is an active low reset to the device. Voltage on the
MCLR/V
PP
pin must not exceed V
DD
to avoid unintended
entering of programming mode.
OSC1/CLKIN 16 18 I ST Oscillator crystal input/external clock source input.
OSC2/CLKOUT 15 17 O Oscillator crystal output. Connects to crystal or resonator in
crystal oscillator mode. In RC mode, OSC2 pin outputs
CLK OUT which has 1/4 the frequency of OSC1, and denotes
the instruction cycle rate.
V
DD
14 15,16 P Positive supply for logic and I/O pins.
V
SS
5 5,6 P Ground reference for logic and I/O pins.
Legend: I = input, O = output, I/O = input/output,
P = power, — = Not Used, TTL = TTL input,
ST = Schmitt Trigger input
PIC16C5X
DS30453B-page 12
Preliminary
1998 Microchip Technology Inc.
TABLE 3-2: PINOUT DESCRIPTION
-
PIC16C55s, PIC16C57s, PIC16CR57s
Name DIP, SOIC
No. SSOP
No. I/O/P
Type Input
Levels Description
RA0
RA1
RA2
RA3
6
7
8
9
5
6
7
8
I/O
I/O
I/O
I/O
TTL
TTL
TTL
TTL
Bi-directional I/O port
RB0
RB1
RB2
RB3
RB4
RB5
RB6
RB7
10
11
12
13
14
15
16
17
9
10
11
12
13
15
16
17
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
TTL
TTL
TTL
TTL
TTL
TTL
TTL
TTL
Bi-directional I/O port
RC0
RC1
RC2
RC3
RC4
RC5
RC6
RC7
18
19
20
21
22
23
24
25
18
19
20
21
22
23
24
25
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
TTL
TTL
TTL
TTL
TTL
TTL
TTL
TTL
Bi-directional I/O port
T0CKI 1 2 I ST Clock input to Timer0. Must be tied to V
SS
or V
DD
if not in use
to reduce current consumption.
MCLR 28 28 I ST Master clear (reset) input. This pin is an active lo w reset to the
device.
OSC1/CLKIN 27 27 I ST Oscillator crystal input/external clock source input.
OSC2/CLKOUT 26 26 O Oscillator crystal output. Connects to crystal or resonator in
crystal oscillator mode. In RC mode, OSC2 pin outputs
CLKOUT which has 1/4 the frequency of OSC1, and denotes
the instruction cycle rate.
V
DD
2 3,4 P Positive supply for logic and I/O pins.
V
SS
4 1,14 P Ground reference for logic and I/O pins.
N/C 3,5 Unused, do not connect
Legend: I = input, O = output, I/O = input/output,
P = power, — = Not Used,
TTL = TTL input, ST = Schmitt Trigger input
1998 Microchip Technology Inc.
Preliminary
DS30453B-page 13
PIC16C5X
3.1 Clocking Scheme/Instruction Cycle
The clock input (OSC1/CLKIN pin) is internally divided
by four to generate four non-overlapping quadrature
clocks namely Q1, Q2, Q3 and Q4. Internally, the
program counter is incremented every Q1, and the
instruction is fetched from program memory and
latched into instruction register in Q4. It is decoded
and executed dur ing the following Q1 through Q4. The
clocks and instruction execution flow is shown in
Figure 3-2 and Example 3-1.
3.2 Instruction Flow/Pipelining
An Instruction Cycle consists of four Q cycles (Q1, Q2,
Q3 and Q4). The instruction fetch and execute are
pipelined such that fetch takes one instruction cycle
while decode and execute takes another instruction
cycle. However, due to the pipelining, each instruction
effectively executes in one cycle. If an instruction
causes the program counter to change (e.g.,
GOTO
)
then two cycles are required to complete the
instruction (Example 3-1).
A fetch cycle begins with the program counter (PC)
incrementing in Q1.
In the execution cycle, the fetched instruction is
latched into the Instruction Register (IR) in cycle Q1.
This instruction is then decoded and executed during
the Q2, Q3, and Q4 cycles. Data memory is read
during Q2 (operand read) and written during Q4
(destination write).
FIGURE 3-2: CLOCK/INSTRUCTION CYCLE
EXAMPLE 3-1: INSTRUCTION PIPELINE FLOW
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
OSC1
Q1
Q2
Q3
Q4
PC
OSC2/CLKOUT
(RC mode)
PC PC+1 PC+2
Fetch INST (PC)
Execute INST (PC-1) Fetch INST (PC+1)
Execute INST (PC) Fetch INST (PC+2)
Execute INST (PC+1)
Internal
phase
clock
All instructions are single cycle, except for any program branches. These take two cycles since the fetch
instruction is “flushed” from the pipeline while the new instruction is being fetched and then executed.
1. MOVLW 55H Fetch 1 Execute 1
2. MOVWF PORTB Fetch 2 Execute 2
3. CALL SUB_1 Fetch 3 Execute 3
4. BSF PORTA, BIT3 Fetch 4 Flush
Fetch SUB_1 Execute SUB_1
PIC16C5X
DS30453B-page 14 Preliminary 1998 Microchip Technology Inc.
NOTES:
1998 Microchip Technology Inc. Preliminary DS30453B-page 15
PIC16C5X
4.0 MEMORY ORGANIZATION
PIC16C5X memory is organized into program memory
and data memory. For devices with more than 512
bytes of program memory, a paging scheme is used.
Program memory pages are accessed using one or
two STATUS register bits. For devices with a data
memory register file of more than 32 registers, a
banking scheme is used. Data memor y banks are
accessed using the File Selection Register (FSR).
4.1 Program Memory Organization
The PIC16C52 has a 9-bit Program Counter (PC)
capable of addressing a 384 x 12 program memory
space (Figure 4-1). The PIC16C54s , PIC16CR54s and
PIC16C55s have a 9-bit Program Counter (PC)
capable of addressing a 512 x 12 program memory
space (Figure 4-2). The PIC16C56s and PIC16CR56s
have a 10-bit Program Counter (PC) capable of
addressing a 1K x 12 program memory space
(Figure 4-3). The PIC16CR57s, PIC16C58s and
PIC16CR58s hav e an 11-bit Prog r am Counter capab le
of addressing a 2K x 12 program memory space
(Figure 4-4). Accessing a location above the physically
implemented address will cause a wraparound.
The reset vector for the PIC16C52 is at 17Fh. A NOP
at the reset vector location will cause a restar t at
location 000h. The reset vector for the PIC16C54s,
PIC16CR54s and PIC16C55s is at 1FFh. The reset
vector for the PIC16C56s and PIC16CR56s is at
3FFh. The reset vector for the PIC16C57s,
PIC16CR57s, PIC16C58s, and PIC16CR58s is at
7FFh.
FIGURE 4-1: PIC16C52 PROGRAM
MEMORY MAP AND STACK
PC<8:0>
Stack Level 1
Stack Level 2
User Memory
Space
9
000h
Reset V ector
On-chip Program
Memory
17Fh
CALL, RETLW
FIGURE 4-2: PIC16C54s/CR54s/C55s
PROGRAM MEMORY MAP
AND STACK
FIGURE 4-3: PIC16C56s/CR56s
PROGRAM MEMORY MAP
AND STACK
PC<8:0>
Stack Level 1
Stack Level 2
User Memory
Space
CALL, RETLW 9
000h
1FFh
Reset V ector
0FFh
100h
On-chip
Program
Memory
PC<9:0>
Stack Level 1
Stack Level 2
User Memory
Space
10
000h
1FFh
Reset V ector
0FFh
100h
On-chip Program
Memory (Page 0)
On-chip Program
Memory (Page 1)
200h
2FFh
300h
3FFh
CALL, RETLW
PIC16C5X
DS30453B-page 16 Preliminary 1998 Microchip Technology Inc.
FIGURE 4-4: PIC16C57s/CR57s/C58s/
CR58s PROGRAM MEMORY
MAP AND STACK
PC<10:0>
Stack Level 1
Stack Level 2
User Memory
Space
11
000h
1FFh
Reset V ector
0FFh
100h
On-chip Program
Memory (Page 0)
On-chip Program
Memory (Page 1)
On-chip Program
Memory (Page 2)
On-chip Program
Memory (Page 3)
200h
3FFh
2FFh
300h
400h
5FFh
4FFh
500h
600h
7FFh
6FFh
700h
CALL, RETLW
1998 Microchip Technology Inc. Preliminary DS30453B-page 17
PIC16C5X
4.2 Data Memory Organization
Data memory is composed of registers, or bytes of
RAM. Therefore, data memor y for a device is specified
by its register file. The register file is divided into two
functional groups: special function registers and
general purpose registers.
The special function registers include the TMR0
register, the Program Counter (PC), the Status
Register, the I/O registers (por ts), and the File Select
Register (FSR). In addition, special pur pose registers
are used to control the I/O port configuration and
prescaler options.
The general purpose registers are used for data and
control information under command of the instructions.
For the PIC16C52, PIC16C54s, PIC16CR54s,
PIC16C56s and PIC16CR56s, the register file is
composed of 7 special function registers and 25
general purpose registers (Figure 4-5).
For the PIC16C55s, the register file is composed of 8
special function registers and 24 general pur pose
registers.
For the PIC16C57s and PIC16CR57s, the register file
is composed of 8 special function registers, 24 general
purpose registers and up to 48 additional general
purpose registers that may be addressed using a
banking scheme (Figure 4-6).
For the PIC16C58s and PIC16CR58s, the register file
is composed of 7 special function registers, 25 general
purpose registers and up to 48 additional general
purpose registers that may be addressed using a
banking scheme (Figure 4-7).
4.2.1 GENERAL PURPOSE REGISTER FILE
The register file is accessed either directly or indirectly
through the file select register FSR (Section 4.7).
FIGURE 4-5: PIC16C52, PIC16C54s,
PIC16CR54s, PIC16C55s,
PIC16C56s, PIC16CR56s
REGISTER FILE MAP
File Address
00h
01h
02h
03h
04h
05h
06h
07h
1Fh
INDF(1)
TMR0
PCL
STATUS
FSR
PORTA
PORTB
General
Purpose
Registers
Note 1: Not a physical register. See Section 4.7
2: PIC16C55s only, others are a general
purpose register.
0Fh
10h
PORTC(2)
PIC16C5X
DS30453B-page 18 Preliminary 1998 Microchip Technology Inc.
FIGURE 4-6: PIC16C57s/CR57s REGISTER FILE MAP
FIGURE 4-7: PIC16C58s/CR58s REGISTER FILE MAP
File Address
00h
01h
02h
03h
04h
05h
06h
07h
1Fh
INDF(1)
TMR0
PCL
STATUS
FSR
PORTA
PORTB
0Fh 10h
Bank 0 Bank 1 Bank 2 Bank 3
3Fh
30h
20h
2Fh
5Fh
50h
40h
4Fh
7Fh
70h
60h
6Fh
General
Purpose
Registers
General
Purpose
Registers
General
Purpose
Registers
General
Purpose
Registers
General
Purpose
Registers
PORTC
08h
Addresses map back to
addresses in Bank 0.
Note 1: Not a physical register. See Section 4.7
FSR<6:5> 00 01 10 11
File Address
00h
01h
02h
03h
04h
05h
06h
07h
1Fh
INDF(1)
TMR0
PCL
STATUS
FSR
PORTA
PORTB
0Fh 10h
Bank 0 Bank 1 Bank 2 Bank 3
3Fh
30h
20h
2Fh
5Fh
50h
40h
4Fh
7Fh
70h
60h
6Fh
General
Purpose
Registers
General
Purpose
Registers
General
Purpose
Registers
General
Purpose
Registers
General
Purpose
Registers
Addresses map back to
addresses in Bank 0.
Note 1: Not a physical register. See Section 4.7
FSR<6:5> 00 01 10 11
1998 Microchip Technology Inc. Preliminary DS30453B-page 19
PIC16C5X
4.2.2 SPECIAL FUNCTION REGISTERS
The Special Function Registers are registers used by
the CPU and peripheral functions to control the
operation of the device (Table 4-1).
The special registers can be classified into two sets.
The special function registers associated with the
“core” functions are descr ibed in this section. Those
related to the operation of the peripheral features are
described in the section for each peripheral feature.
TABLE 4-1: SPECIAL FUNCTION REGISTER SUMMARY
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-On
Reset
Value on
MCLR and
WDT Reset
N/A TRIS I/O control registers (TRISA, TRISB, TRISC) 1111 1111 1111 1111
N/A OPTION Contains control bits to configure Timer0 and Timer0/WDT prescaler --11 1111 --11 1111
00h INDF Uses contents of FSR to address data memory (not a physical register) xxxx xxxx uuuu uuuu
01h TMR0 8-bit real-time clock/counter xxxx xxxx uuuu uuuu
02h(1) PCL Low order 8 bits of PC 1111 1111 1111 1111
03h STATUS PA2 PA1 PA0 TO PD ZDCC0001 1xxx 000q quuu
04h FSR Indirect data memory address pointer 1xxx xxxx 1uuu uuuu
05h PORTA RA3 RA2 RA1 RA0 ---- xxxx ---- uuuu
06h PORTB RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0 xxxx xxxx uuuu uuuu
07h(2) PORTC RC7 RC6 RC5 RC4 RC3 RC2 RC1 RC0 xxxx xxxx uuuu uuuu
Legend: Shaded boxes = unimplemented or unused, = unimplemented, read as '0' (if applicable)
x = unknown, u = unchanged, q = see the tables in Section 7.7 for possible values.
Note 1: The upper byte of the Program Counter is not directly accessible. See Section 4.5
for an explanation of how to access these bits.
2: File address 07h is a general purpose register on the PIC16C52, PIC16C54s, PIC16CR54s, PIC16C56s, PIC16CR56s,
PIC16C58s and PIC16CR58s.
PIC16C5X
DS30453B-page 20 Preliminary 1998 Microchip Technology Inc.
4.3 STATUS Register
This register contains the arithmetic status of the ALU,
the RESET status, and the page preselect bits for
program memories larger than 512 words.
The STATUS register can be the destination for any
instruction, as with any other register. If the STATUS
register is the destination for an instruction that affects
the Z, DC or C bits, then the write to these three bits is
disabled. These bits are set or cleared according to
the device logic. Furthermore, the TO and PD bits are
not writable. Therefore, the result of an instruction with
the STATUS register as destination may be different
than intended.
For example, CLRF STATUS will clear the upper three
bits and set the Z bit. This leaves the STATUS register
as 000u u1uu (where u = unchanged).
It is recommended, therefore, that only BCF, BSF and
MOVWF instructions be used to alter the STATUS
register because these instructions do not affect the Z,
DC or C bits from the STATUS register. For other
instructions, which do affect STATUS bits, see
Section 8.0, Instruction Set Summary.
FIGURE 4-8: STATUS REGISTER (ADDRESS:03h)
R/W-0 R/W-0 R/W-0 R-1 R-1 R/W-x R/W-x R/W-x
PA2 PA1 PA0 TO PD Z DC C R = Readable bit
W = Writable bit
- n = Value at POR reset
bit7 6 5 4 3 2 1 bit0
bit 7: PA2: This bit unused at this time.
Use of the PA2 bit as a general purpose read/write bit is not recommended, since this may affect upward
compatibility with future products.
bit 6-5: PA1:PA0: Program page preselect bits (PIC16C56s/CR56s)(PIC16C57s/CR57s)(PIC16C58s/CR58s)
00 = Page 0 (000h - 1FFh) - PIC16C56s/CR56s, PIC16C57s/CR57s, PIC16C58s/CR58s
01 = Page 1 (200h - 3FFh) - PIC16C56s/CR56s, PIC16C57s/CR57s, PIC16C58s/CR58s
10 = Page 2 (400h - 5FFh) - PIC16C57s/CR57s, PIC16C58s/CR58s
11 = Page 3 (600h - 7FFh) - PIC16C57s/CR57s, PIC16C58s/CR58s
Each page is 512 words.
Using the PA1:PA0 bits as general purpose read/write bits in devices which do not use them for program
page preselect is not recommended since this may affect upward compatibility with future products.
bit 4: TO: Time-out bit
1 = After power-up, CLRWDT instruction, or SLEEP instruction
0 = A WDT time-out occurred
bit 3: PD: Power-down bit
1 = After power-up or by the CLRWDT instruction
0 = By execution of the SLEEP instruction
bit 2: Z: Zero bit
1 = The result of an arithmetic or logic operation is zero
0 = The result of an arithmetic or logic operation is not zero
bit 1: DC: Digit carry/borrow bit (for ADDWF and SUBWF instructions)
ADDWF
1 = A carry from the 4th low order bit of the result occurred
0 = A carry from the 4th low order bit of the result did not occur
SUBWF
1 = A borrow from the 4th low order bit of the result did not occur
0 = A borrow from the 4th low order bit of the result occurred
bit 0: C: Carry/borrow bit (for ADDWF, SUBWF and RRF, RLF instructions)
ADDWF SUBWF RRF or RLF
1 = A carry occurred 1 = A borrow did not occur Load bit with LSb or MSb, respectively
0 = A carry did not occur 0 = A borrow occurred
1998 Microchip Technology Inc. Preliminary DS30453B-page 21
PIC16C5X
4.4 OPTION Register
The OPTION register is a 6-bit wide, write-only
register which contains various control bits to
configure the Timer0/WDT prescaler and Timer0.
By executing the OPTION instruction, the contents of
the W register will be transferred to the OPTION
register. A RESET sets the OPTION<5:0> bits.
FIGURE 4-9: OPTION REGISTER
U-0 U-0 W-1 W-1 W-1 W-1 W-1 W-1
T0CS T0SE PSA PS2 PS1 PS0 W = Writable bit
U = Unimplemented bit
- n = Value at POR reset
bit7 6 5 4 3 2 1 bit0
bit 7-6: Unimplemented.
bit 5: T0CS: Timer0 clock source select bit
1 = Transition on T0CKI pin
0 = Internal instruction cycle clock (CLKOUT)
bit 4: T0SE: Timer0 source edge select bit
1 = Increment on high-to-low transition on T0CKI pin
0 = Increment on low-to-high transition on T0CKI pin
bit 3: PSA: Prescaler assignment bit
1 = Prescaler assigned to the WDT (not implemented on PIC16C52)
0 = Prescaler assigned to Timer0
bit 2-0: PS2:PS0: Prescaler rate select bits
000
001
010
011
100
101
110
111
1 : 2
1 : 4
1 : 8
1 : 16
1 : 32
1 : 64
1 : 128
1 : 256
1 : 1
1 : 2
1 : 4
1 : 8
1 : 16
1 : 32
1 : 64
1 : 128
Bit Value Timer0 Rate WDT Rate (not implemented on PIC16C52)
PIC16C5X
DS30453B-page 22 Preliminary 1998 Microchip Technology Inc.
4.5 Program Counter
As a program instruction is executed, the Program
Counter (PC) will contain the address of the next
program instruction to be executed. The PC value is
increased by one every instruction cycle, unless an
instruction changes the PC.
For a GOTO instruction, bits 8:0 of the PC are provided
by the GOTO instruction word. The PC Latch (PCL) is
mapped to PC<7:0> (Figure 4-10 and Figure 4-11).
For the PIC16C56s, PIC16CR56s, PIC16C57s,
PIC16CR57s, PIC16C58s and PIC16CR58s, a page
number must be supplied as well. Bit5 and bit6 of the
STATUS register provide page infor mation to bit9 and
bit10 of the PC (Figure 4-11 and Figure 4-12).
For a CALL instr uction, or any instruction where the
PCL is the destination, bits 7:0 of the PC again are
provided by the instruction word. However, PC<8>
does not come from the instruction word, but is always
cleared (Figure 4-10 and Figure 4-11).
Instructions where the PCL is the destination, or
Modify PCL instructions, include MOVWF PC, ADDWF
PC, and BSF PC,5.
For the PIC16C56s, PIC16CR56s, PIC16C57s,
PIC16CR57s, PIC16C58s and PIC16CR58s, a page
number again must be supplied. Bit5 and bit6 of the
STATUS register provide page infor mation to bit9 and
bit10 of the PC (Figure 4-11 and Figure 4-12).
Note: Because PC<8> is cleared in the CALL
instruction, or any Modify PCL instruction,
all subroutine calls or computed jumps are
limited to the first 256 locations of any pro-
gram memory page (512 words long).
FIGURE 4-10: LOADING OF PC
BRANCH INSTRUCTIONS -
PIC16C52, PIC16C54s,
PIC16CR54s, PIC16C55s
FIGURE 4-11: LOADING OF PC
BRANCH INSTRUCTIONS -
PIC16C56s/PIC16CR56s
PC 87 0
PCL
PC 87 0
PCL
Reset to '0'
Instruction Word
Instruction Word
GOTO Instruction
CALL or Modify PCL Instruction
PA1:PA0
2
STATUS
PC 87 0
PCL
910
PA1:PA0
2
STATUS
PC 87 0
PCL
910
Instruction Word
Reset to ‘0’
Instruction Word
70
70
GOTO Instruction
CALL or Modify PCL Instruction
1998 Microchip Technology Inc. Preliminary DS30453B-page 23
PIC16C5X
FIGURE 4-12: LOADING OF PC
BRANCH INSTRUCTIONS -
PIC16C57s/PIC16CR57s, AND
PIC16C58s/PIC16CR58s
PA1:PA0
2
STATUS
PC 87 0
PCL
910
PA1:PA0
2
STATUS
PC 87 0
PCL
910
Instruction Word
Reset to ‘0’
Instruction Word
70
70
GOTO Instruction
CALL or Modify PCL Instruction
4.5.1 PAGING CONSIDERATIONS –
PIC16C56s/CR56s, PIC16C57s/CR57s AND
PIC16C58s/CR58s
If the Program Counter is pointing to the last address
of a selected memory page, when it increments it will
cause the program to continue in the next higher page.
However, the page preselect bits in the STATUS
register will not be updated. Therefore, the next GOTO,
CALL, or Modify PCL instruction will send the program
to the page specified by the page preselect bits (PA0
or PA1:PA0).
For example, a NOP at location 1FFh (page 0)
increments the PC to 200h (page 1). A GOTO xxx at
200h will return the program to address 0xxh on page
0 (assuming that PA1:PA0 are clear).
To prevent this, the page preselect bits must be
updated under program control.
4.5.2 EFFECTS OF RESET
The Program Counter is set upon a RESET, which
means that the PC addresses the last location in the
last page i.e., the reset vector.
The STATUS register page preselect bits are cleared
upon a RESET, which means that page 0 is
pre-selected.
Therefore, upon a RESET, a GOTO instruction at the
reset vector location will automatically cause the
program to jump to page 0.
4.6 Stack
PIC16C5X devices have a 9-bit, 10-bit or 11-bit wide,
two-level hardware push/pop stack (Figure 4-2,
Figure 4-1, and Figure 4-3 respectively).
A CALL instr uction will
push
the current value of stack
1 into stack 2 and then push the current program
counter value , incremented b y one , into stac k le v el 1. If
more than two sequential CALL’s are executed, only
the most recent two return addresses are stored.
A RETLW instruction will
pop
the contents of stack level
1 into the program counter and then copy stack level 2
contents into level 1. If more than two sequential
RETLWs are executed, the stack will be filled with the
address previously stored in level 2. Note that the
W register will be loaded with the literal value specified
in the instruction. This is par ticularly useful for the
implementation of data look-up tables within the
program memory.
For the RETLW instr uction, the PC is loaded with the
Top Of Stack (TOS) contents. All of the devices
covered in this data sheet have a two-level stack. The
stack has the same bit width as the device PC.
PIC16C5X
DS30453B-page 24 Preliminary 1998 Microchip Technology Inc.
4.7 Indirect Data Addressing; INDF and
FSR Registers
The INDF register is not a physical register.
Addressing INDF actually addresses the register
whose address is contained in the FSR register (FSR
is a
pointer
). This is indirect addressing.
EXAMPLE 4-1: INDIRECT ADDRESSING
Register file 05 contains the value 10h
Register file 06 contains the value 0Ah
Load the value 05 into the FSR register
A read of the INDF register will return the value
of 10h
Increment the value of the FSR register by one
(FSR = 06h)
A read of the INDR register now will return the
value of 0Ah.
Reading INDF itself indirectly (FSR = 0) will produce
00h. Writing to the INDF register indirectly results in a
no-operation (although STATUS bits may be affected).
A simple program to clear RAM locations 10h-1Fh
using indirect addressing is shown in Example 4-2.
EXAMPLE 4-2: HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
movlw 0x10 ;initialize pointer
movwf FSR ; to RAM
NEXT clrf INDF ;clear INDF register
incf FSR,F ;inc pointer
btfsc FSR,4 ;all done?
goto NEXT ;NO, clear next
CONTINUE : ;YES, continue
The FSR is either a 5-bit (PIC16C52, PIC16C54s,
PIC16CR54s, PIC16C55s), 6-bit (PIC16C56s,
PIC16CR56s), or 7-bit (PIC16C57s, PIC16CR57s,
PIC16C58s, PIC16CR58s) wide register. It is used in
conjunction with the INDF register to indirectly address
the data memory area.
The FSR<4:0> bits are used to select data memory
addresses 00h to 1Fh.
PIC16C52, PIC16C54s, PIC16CR54s, PIC16C55s:
These do not use banking. FSR<6:5> are
unimplemented and read as '1's.
PIC16C57s, PIC16CR57s, PIC16C58s,
PIC16CR58s: FSR<6:5> are the bank select bits and
are used to select the bank to be addressed (00 =
bank 0, 01 = bank 1, 10 = bank 2, 11 = bank 3).
FIGURE 4-13: DIRECT/INDIRECT ADDRESSING
Note 1: For register map detail see Section 4.2.
bank location select
location select
bank select
Indirect Addressing
Direct Addressing
Data
Memory(1) 0Fh
10h
Bank 0 Bank 1 Bank 2 Bank 3
0
4
5
6(FSR)
1000 01 11
00h
1Fh 3Fh 5Fh 7Fh
(opcode) 04
5
6
(FSR)
Addresses map back
to addresses in Bank 0.
1998 Microchip Technology Inc. Preliminary DS30453B-page 25
PIC16C5X
5.0 I/O PORTS
As with any other register, the I/O registers can be
written and read under program control. Howe v er, read
instructions (e.g., MOVF PORTB,W) always read the I/O
pins independent of the pin’s input/output modes. On
RESET, all I/O ports are defined as input (inputs are at
hi-impedance) since the I/O control registers (TRISA,
TRISB, TRISC) are all set.
5.1 PORTA
PORTA is a 4-bit I/O register. Only the low order 4 bits
are used (RA3:RA0). Bits 7-4 are unimplemented and
read as '0's.
5.2 PORTB
PORTB is an 8-bit I/O register (PORTB<7:0>).
5.3 PORTC
PORTC is an 8-bit I/O register for PIC16C55s,
PIC16C57s and PIC16CR57s.
PORTC is a general purpose register for PIC16C52,
PIC16C54s, PIC16CR54s, PIC16C56s, PIC16C58s
and PIC16CR58s.
5.4 TRIS Registers
The output driver control registers are loaded with the
contents of the W register by executing the TRIS f
instruction. A '1' from a TRIS register bit puts the
corresponding output driver in a hi-impedance mode.
A '0' puts the contents of the output data latch on the
selected pins, enabling the output buffer.
The TRIS registers are “write-only” and are set (output
drivers disabled) upon RESET.
Note: A read of the por ts reads the pins, not the
output data latches. That is, if an output
driver on a pin is enabled and driven high,
but the external system is holding it low, a
read of the por t will indicate that the pin is
low.
5.5 I/O Interfacing
The equivalent circuit for an I/O port pin is shown in
Figure 5-1. All ports may be used for both input and
output operation. For input operations these ports are
non-latching. Any input must be present until read by
an input instruction (e.g., MOVF PORTB, W). The
outputs are latched and remain unchanged until the
output latch is rewritten. To use a port pin as output,
the corresponding direction control bit (in TRISA,
TRISB) must be cleared (= 0). For use as an input, the
corresponding TRIS bit must be set. Any I/O pin can
be programmed individually as input or output.
FIGURE 5-1: EQUIVALENT CIRCUIT
FOR A SINGLE I/O PIN
Note 1: I/O pins have protection diodes to VDD and VSS.
Data
Bus
QD
Q
CK
QD
Q
CK P
N
WR
Port
TRIS ‘f
Data
TRIS
RD Port
VSS
VDD
I/O
pin(1)
W
Reg
Latch
Latch
Reset
TABLE 5-1: SUMMARY OF PORT REGISTERS
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-On
Reset
Value on
MCLR and
WDT Reset
N/A TRIS I/O control registers (TRISA, TRISB, TRISC) 1111 1111 1111 1111
05h PORTA RA3 RA2 RA1 RA0 ---- xxxx ---- uuuu
06h PORTB RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0 xxxx xxxx uuuu uuuu
07h PORTC RC7 RC6 RC5 RC4 RC3 RC2 RC1 RC0 xxxx xxxx uuuu uuuu
Legend: Shaded boxes = unimplemented, read as ‘0’,
= unimplemented, read as '0', x = unknown, u = unchanged
PIC16C5X
DS30453B-page 26 Preliminary 1998 Microchip Technology Inc.
5.6 I/O Programming Considerations
5.6.1 BI-DIRECTIONAL I/O PORTS
Some instructions operate internally as read followed
by write operations. The BCF and BSF instructions, for
example, read the entire port into the CPU, execute
the bit operation and re-write the result. Caution must
be used when these instructions are applied to a por t
where one or more pins are used as input/outputs. For
example, a BSF operation on bit5 of PORTB will cause
all eight bits of PORTB to be read into the CPU, bit5 to
be set and the PORTB v alue to be written to the output
latches. If another bit of PORTB is used as a
bi-directional I/O pin (say bit0) and it is defined as an
input at this time, the input signal present on the pin
itself would be read into the CPU and rewritten to the
data latch of this particular pin, overwriting the
previous content. As long as the pin stays in the input
mode, no problem occurs. However, if bit0 is switched
into output mode later on, the content of the data latch
may now be unknown.
Example 5-1 shows the effect of two sequential
read-modify-write instructions (e.g., BCF, BSF, etc.) on
an I/O port.
A pin actively outputting a high or a low should not be
driven from external devices at the same time in order
to change the lev el on this pin (“wired-or”, “wired-and”).
The resulting high output currents may damage the
chip.
EXAMPLE 5-1: READ-MODIFY-WRITE
INSTRUCTIONS ON AN
I/O PORT
;Initial PORT Settings
; PORTB<7:4> Inputs
; PORTB<3:0> Outputs
;PORTB<7:6> have external pull-ups and are
;not connected to other circuitry
;
; PORT latch PORT pins
; ---------- ----------
BCF PORTB, 7 ;01pp pppp 11pp pppp
BCF PORTB, 6 ;10pp pppp 11pp pppp
MOVLW 03Fh ;
TRIS PORTB ;10pp pppp 10pp pppp
;
;Note that the user may have expected the pin
;values to be 00pp pppp. The 2nd BCF caused
;RB7 to be latched as the pin value (High).
5.6.2 SUCCESSIVE OPERATIONS ON I/O
PORTS
The actual write to an I/O por t happens at the end of
an instruction cycle, whereas for reading, the data
must be valid at the beginning of the instruction cycle
(Figure 5-2). Therefore, care must be exercised if a
write followed by a read operation is carried out on the
same I/O port. The sequence of instructions should
allow the pin voltage to stabilize (load dependent)
before the next instruction, which causes that file to be
read into the CPU, is executed. Otherwise, the
previous state of that pin may be read into the CPU
rather than the new state. When in doubt, it is better to
separate these instructions with a NOP or another
instruction not accessing this I/O port.
FIGURE 5-2: SUCCESSIVE I/O OPERATION
PC PC + 1 PC + 2 PC + 3
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
Instruction
fetched
RB7:RB0
MOVWF PORTB NOP
Port pin
sampled here
NOP
MOVF PORTB,W
Instruction
executed MOVWF PORTB
(Write to
PORTB)
NOP
MOVF PORTB,W
This example shows a write
to PORTB followed by a read
from PORTB.
(Read
PORTB)
Port pin
written here