Microchip Technology Inc PIC16CR54C-04-P, PIC16CR54C-04-SO, PIC16CR54C-04-SS, PIC16CR54C-04I-P, PIC16CR54C-04I-SO Datasheet

M



1998 Microchip Technology Inc.

Preliminary

DS40191A-page 1

PIC16CR54C

Devices Included in this Data Sheet:

• PIC16CR54C

High-Performance RISC CPU:

• Only 33 single word instructions to learn

• All instructions are single cycle (200 ns) except for
program branches which are two-cycle

• Operating speed: DC - 20 MHz clock input

DC - 200 ns instruction cycle

• 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 Tec hnology:

• Low-power, high-speed CMOS ROM technology

• Fully static design

• Wide-operating voltage and temperature range:

- ROM Commercial/Industrial 3.0V to 5.5V

• Low-power consumption

- < 2 mA typical @ 5V, 4 MHz

- 15 µA typical @ 3V, 32 kHz

- < 0.6 µA typical standby current

(with WDT disabled) @ 3V, 0°C to 70°C

Device Pins I/O ROM RAM

PIC16CR54C 18 12 512 25

Pin Diagrams

PDIP and SOIC

PIC16CR54C

RA1
RA0
OSC1/CLKIN
OSC2/CLKOUT
V

DD

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

PIC16CR54C

RA2
RA3

T0CKI

MCLR

VPP

VSS
RB0
RB1
RB2

RB3

•1
2
3
4
5
6
7
8
9

10

18
17
16
15
14
13
12

11

RA1
RA0
OSC1/CLKIN
OSC2/CLKOUT
V

DD

RB7
RB6
RB5
RB4

ROM-Based 8-Bit CMOS Microcontroller Series

PIC16CR54C

DS40191A-page 2

Preliminary



1998 Microchip Technology Inc.

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 3.0-5.5 User See Note 1 0.7 PIC16CR54B

or

PIC16CR54C

Yes

PIC16C55 2.5-6.25 Factory See Note 1 1.7 — No
PIC16C55A 3.0-5.5 User See Note 1 0.7 — Yes
PIC16C56 2.5-6.25 Factory See Note 1 1.7 — No
PIC16C56A 3.0-5.5 User See Note 1 0.7 PIC16CR56A Yes
PIC16C57 2.5-6.25 Factory See Note 1 1.2 — No
PIC16C57C 3.0-5.5 User See Note 1 0.7 PIC16CR57C Yes
PIC16CR57C 2.5-5.5 Factory See Note 1 0.7 NA Yes
PIC16C58A 2.0-6.25 User See Note 1 0.9 PIC16CR58A

No

(2)

PIC16C58B 3.0-5.5 User See Note 1 0.7 PIC16CR58B Yes
PIC16CR54A 2.5-6.25 Factory See Note 1 1.2 NA Yes
PIC16CR54B 2.5-5.5 Factory See Note 1 0.7 NA Yes
PIC16CR54C 3.0-5.5 Factory See Note 1 0.7 NA Yes
PIC16CR56A 2.5-5.5 Factory See Note 1 0.7 NA Yes
PIC16CR57B 2.5-6.25 Factory See Note 1 0.9 NA Yes
PIC16CR58A 2.5-6.25 Factory See Note 1 0.9 NA Yes
PIC16CR58B 2.5-5.5 Factory See Note 1 0.7 NA Yes



1998 Microchip Technology Inc.

Preliminary

DS40191A-page 3

PIC16CR54C

Table of Contents

1.0 General Description.............................................................................................................................................5

2.0 PIC16C5X Device Varieties.................................................................................................................................7

3.0 Architectural Overview.........................................................................................................................................9

4.0 Memory Organization........................................................................................................................................13

5.0 I/O Ports ............................................................................................................................................................ 19

6.0 Timer0 Module and TMR0 Register .................................................................................................................. 21

7.0 Special Features of the CPU.............................................................................................................................25

8.0 Instruction Set Summary...................................................................................................................................37

9.0 Development Support........................................................................................................................................49

10.0 Electrical Characteristics - PIC16CR54C..........................................................................................................53

11.0 DC and AC Characteristics - PIC16CR54C.......................................................................................................63

12.0 Packaging Information.......................................................................................................................................73

Appendix A: Compatibility.............................................................................................................................................77

Index ............................................................................................................................................................................79

On-Line Support............................................................................................................................................................81

Reader Response.........................................................................................................................................................82

PIC16CR54C Product Identification System.................................................................................................................83

PIC16CR54C

DS40191A-page 4

Preliminary



1998 Microchip Technology Inc.

NOTES:



1998 Microchip Technology Inc.

Preliminary

DS40191A-page 5

PIC16CR54C

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 sin­gle cycle (200 ns) except for program branches which
take two cycles. The PIC16C5X delivers performance
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 f ea­tures 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 configurations 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 packaged versions 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 assembler , 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 perf ectly in applications rang­ing from high-speed automotive and appliance motor
control to low-power remote transmitters/receivers,
pointing devices and telecom processors. The EPROM
technology makes customizing application programs
(transmitter codes, motor speeds, receiver frequen­cies, etc.) extremely fast and convenient. The small
footprint packages, for through hole or surface mount­ing, make this microcontroller series perfect for applica­tions with space limitations. Low-cost, low-power, high
performance, ease of use and I/O flexibility make the
PIC16C5X series very versatile even in areas where no
microcontroller use has been considered before (e.g.,
timer functions, replacement of “glue” logic in larger
systems, coprocessor applications).

PIC16CR54C

DS40191A-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)

4 20 20 20 20

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™ Family de vices ha v e Power-on Reset, selectable 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™ Family de vices ha v e Power-on Reset, selectable Watchdog Timer (except PIC16C52), selectab le code
protect and high I/O current capability.



1998 Microchip Technology Inc.

Preliminary

DS40191A-page 7

PIC16CR54C

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 PIC16CR54C 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 U

V 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 PIC16CR54C. Third party
programmers also are available; refer to the Third
Party Guide for a list of sources.

2.2 One-Time-Pr

ogrammable (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 Quic

k-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 Serializ

ed
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 Onl

y 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

PIC16CR54C

DS40191A-page 8

Preliminary



1998 Microchip Technology Inc.

NOTES:



1998 Microchip Technology Inc.

Preliminary

DS40191A-page 9

PIC16CR54C

3.0 ARCHITECTURAL OVERVIEW

The high performance of the PIC16CR54C can be
attributed to a number of architectural features
commonly found in RISC microprocessors. To begin
with, the PIC16CR54C 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 have 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 PIC16CR54C address 512 x 12 of program
memory. All program memory is internal.

The PIC16CR54C 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 PIC16CR54C 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 PIC16CR54C simple yet
efficient. In addition, the learning curve is reduced
significantly.

The PIC16CR54C 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 borr

ow 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.

PIC16CR54C

DS40191A-page 10

Preliminary



1998 Microchip Technology Inc.

FIGURE 3-1: PIC16CR54C SERIES BLOCK DIAGRAM

WDT TIME

OUT

8

STACK 1
STACK 2

ROM

512 X 12

INSTRUCTION

REGISTER

INSTRUCTION

DECODER

WA TCHDOG

TIMER

CONFIGURA TION WORD

OSCILLA TOR/

TIMING &

CONTROL

GENERAL
PURPOSE
REGISTER

FILE

(SRAM)

25 Bytes

WDT/TMR0

PRESCALER

OPTION REG.

“OPTION”

“SLEEP”

“CODE

PROTECT”

“OSC

SELECT”

DIRECT ADDRESS

TMR0

FROM W

FROM W

“TRIS 5”

“TRIS 6”

FSR

TRISA PORTA

TRISB PORTB

T0CKI

PIN

9-11

9-11

12

12

8

W

4

4

4

DATA BUS

8

8

8

8

ALU

STATUS

FROM W

CLKOUT

8

9

6

5

OSC1 OSC2 MCLR

LITERALS

PC

“DISABLE”

2

RA3:RA0 RB7:RB0

DIRECT RAM

ADDRESS



1998 Microchip Technology Inc.

Preliminary

DS40191A-page 11

PIC16CR54C

TABLE 3-1: PINOUT DESCRIPTION - PIC16CR54C

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/verify voltage input. This pin is an

active low reset to the device.

OSC1/CLKIN 16 18 I ST

(1)

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
CLKOUT 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

Note 1:

Schmitt Trigger input only when in RC mode.

PIC16CR54C

DS40191A-page 12

Preliminary



1998 Microchip Technology Inc.

3.1 Cloc

king 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 during the following Q1 through Q4. The
clocks and instruction execution flow is shown in
Figure 3-2 and Example 3-1.

3.2 Instruction Flo

w/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



1998 Microchip Technology Inc.

Preliminary

DS40191A-page 13

PIC16CR54C

4.0 MEMORY ORGANIZATION

PIC16CR54C 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 memory banks are
accessed using the File Selection Register (FSR).

4.1 Pr

ogram Memory Organization

The PIC16CR54C has a 9-bit Program Counter (PC)
capable of addressing a 512 x 12 program memory
space (Figure 4-1). Accessing a location above the
physically implemented address will cause a
wraparound.

The reset vector for the PIC16CR54C is at 1FFh. A
NOP at the reset vector location will cause a restart at
location 000h.

FIGURE 4-1: PIC16CR54C PROGRAM

MEMORY MAP AND STACK

4.2 Data Memor

y Organization

Data memory is composed of registers, or bytes of
RAM. Therefore, data memory 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 (ports), and the File Select
Register (FSR). In addition, special purpose 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 PIC16CR54C, the register file is composed of
7 special function registers and 25 general purpose
registers (Figure 4-2).

PC<8:0>

Stack Level 1
Stack Level 2

User Memory

Space

CALL, RETLW

9

000h

1FFh

Reset Vector

0FFh
100h

On-chip
Program
Memory

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 4-2: PIC16CR54C REGISTER FILE

MAP

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 described in this section. Those
related to the operation of the peripheral features are
described in the section for each peripheral feature.

File Address

00h
01h
02h
03h
04h
05h
06h

1Fh

INDF

(1)

TMR0

PCL

STATUS

FSR

PORTA

PORTB

General

Purpose

Registers

Note 1: Not a physical register. See Section 4.7

0Fh
10h

07h

PIC16CR54C

DS40191A-page 14

Preliminary



1998 Microchip Technology Inc.

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)

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 Z DC C

0001 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
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.

 1998 Microchip Technology Inc. Preliminary DS40191A-page 15

PIC16CR54C

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. Further more, the T

O 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 4-3: 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: Not Applicable
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

PIC16CR54C

DS40191A-page 16 Preliminary  1998 Microchip Technology Inc.

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 4-4: 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)

 1998 Microchip Technology Inc. Preliminary DS40191A-page 17

PIC16CR54C

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 4-5 and Figure 4-6).

For a CALL instruction, 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.

.

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 pro­gram memory page (512 words long).

FIGURE 4-5: LOADING OF PC

BRANCH INSTRUCTIONS ­PIC16CR54C

4.5.1 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

PIC16CR54C device has a 9-bit, two-level hardware
push/pop stack (Figure 4-1).

A CALL instruction will

push

the current value of stack
1 into stack 2 and then push the current program
counter value, incremented by 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
RETLW’s 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 particularly useful for the
implementation of data look-up tables within the
program memory.

PC

8 7 0

PCL

PC

8 7 0

PCL

Reset to '0'

Instruction Word

Instruction Word

GOTO Instruction

CALL or Modify PCL Instruction

PIC16CR54C

DS40191A-page 18 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 = 06)

• 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 a 5-bit ( PIC16CR54C) 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.

PIC16CR54C: Do not use banking. FSR<6:5> are
unimplemented and read as '1's.

FIGURE 4-6: DIRECT/INDIRECT ADDRESSING

Note 1: For register map detail see Section 4.2.

bank

location select

location select

bank select

Indirect AddressingDirect Addressing

Data
Memory

(1)

0Fh
10h

Bank 0

0

4

5

6

(FSR)

00

00h

1Fh

(opcode) 04

5

6

(FSR)

 1998 Microchip Technology Inc. Preliminary DS40191A-page 19

PIC16CR54C

5.0 I/O PORTS

As with any other register, the I/O registers can be
written and read under program control. Ho wever, 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 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.

5.4 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

Note: A read of the ports 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 port will indicate that the pin is
low.

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) 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
Legend: Shaded boxes = unimplemented, read as ‘0’,

– = unimplemented, read as '0', x = unknown, u = unchanged

PIC16CR54C

DS40191A-page 20 Preliminary  1998 Microchip Technology Inc.

5.5 I/O Programming Considerations

5.5.1 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 port
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 value 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 level 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).

5.5.2 SUCCESSIVE OPERATIONS ON I/O
PORTS

The actual write to an I/O port 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

 1998 Microchip Technology Inc. Preliminary DS40191A-page 21

PIC16CR54C

6.0 TIMER0 MODULE AND
TMR0 REGISTER

The Timer0 module has the following features:

• 8-bit timer/counter register, TMR0

- Readable and writable

• 8-bit software programmable prescaler

• Internal or external clock select

- Edge select for external clock

Figure 6-1 is a simplified block diagram of the Timer0
module, while Figure 6-2 shows the electrical structure
of the Timer0 input.

Timer mode is selected by clearing the T0CS bit
(OPTION<5>). In timer mode, the Timer0 module will
increment every instruction cycle (without prescaler). If
TMR0 register is written, the increment is inhibited for
the following two cycles (Figure 6-3 and Figure 6-4).
The user can work around this by writing an adjusted
value to the TMR0 register.

Counter mode is selected by setting the T0CS bit
(OPTION<5>). In this mode, Timer0 will increment
either on every rising or falling edge of pin T0CKI. The
incrementing edge is determined by the source edge
select bit T0SE (OPTION<4>). Clearing the T0SE bit
selects the rising edge. Restrictions on the external
clock input are discussed in detail in Section 6.1.

The prescaler may be used by either the Timer0
module or the Watchdog Timer, but not both. The
prescaler assignment is controlled in software by the
control bit PSA (OPTION<3>). Clearing the PSA bit
will assign the prescaler to Timer0. The prescaler is
not readable or writable. When the prescaler is
assigned to the Timer0 module, prescale v alues of 1:2,
1:4,..., 1:256 are selectable. Section 6.2 details the
operation of the prescaler.

A summary of registers associated with the Timer0
module is found in Table 6-1.

FIGURE 6-1: TIMER0 BLOCK DIAGRAM

FIGURE 6-2: ELECTRICAL STRUCTURE OF T0CKI PIN

Note 1: Bits T0CS, T0SE, PSA, PS2, PS1 and PS0 are located in the OPTION register.

2: The prescaler is shared with the Watchdog Timer (Figure 6-6).

T0CKI

T0SE

(1)

0

1

1

0

pin

T0CS

(1)

FOSC/4

Programmable

Prescaler

(2)

Sync with

Internal

Clocks

TMR0 reg

PSout

(2 cycle delay)

PSout

Data bus

8

PSA

(1)

PS2, PS1, PS0

(1)

3

Sync

VSS

VSS

RIN

Schmitt Trigger

N

Input Buffer

T0CKI

pin

Note 1: ESD protection circuits

(1)

(1)

PIC16CR54C

DS40191A-page 22 Preliminary  1998 Microchip Technology Inc.

FIGURE 6-3: TIMER0 TIMING: INTERNAL CLOCK/NO PRESCALE

FIGURE 6-4: TIMER0 TIMING: INTERNAL CLOCK/PRESCALE 1:2

TABLE 6-1: REGISTERS ASSOCIATED WITH TIMER0

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

01h TMR0 Timer0 - 8-bit real-time clock/counter xxxx xxxx uuuu uuuu
N/A OPTION

— — T0CS T0SE PSA PS2 PS1 PS0 --11 1111 --11 1111

Legend: Shaded cells: Unimplemented bits,

- = unimplemented, x = unknown, u = unchanged,

PC-1

Q1 Q2 Q3 Q4

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

PC
(Program
Counter)

Instruction
Fetch

Timer0

PC PC+1 PC+2 PC+3 PC+4 PC+5 PC+6

T0

T0+1 T0+2 NT0 NT0 NT0 NT0+1 NT0+2

MOVWF TMR0

MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W

Write TMR0
executed

Read TMR0
reads NT0

Read TMR0
reads NT0

Read TMR0
reads NT0

Read TMR0
reads NT0 + 1

Read TMR0
reads NT0 + 2

Instruction
Executed

PC-1

Q1 Q2 Q3 Q4

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

PC
(Program
Counter)

Instruction
Fetch

Timer0

PC PC+1 PC+2 PC+3 PC+4 PC+5 PC+6

T0 NT0+1

MOVWF TMR0

MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W

Write TMR0
executed

Read TMR0
reads NT0

Read TMR0
reads NT0

Read TMR0
reads NT0

Read TMR0
reads NT0

Read TMR0
reads NT0 + 1

T0+1

NT0

Instruction
Execute

T

0

 1998 Microchip Technology Inc. Preliminary DS40191A-page 23

PIC16CR54C

6.1 Using Timer0 with an External Clock

When an external clock input is used for Timer0, it
must meet certain requirements. The external clock
requirement is due to internal phase clock (T

OSC)

synchronization. Also, there is a delay in the actual
incrementing of Timer0 after synchronization.

6.1.1 EXTERNAL CLOCK SYNCHRONIZATION

When no prescaler is used, the external clock input is
the same as the prescaler output. The synchronization
of T0CKI with the internal phase clocks is
accomplished by sampling the prescaler output on the
Q2 and Q4 cycles of the internal phase clocks
(Figure 6-5). Therefore, it is necessary for T0CKI to be
high for at least 2T

OSC (and a small RC delay of 20 ns)

and low for at least 2T

OSC (and a small RC delay of

20 ns). Refer to the electrical specification of the
desired device.

When a prescaler is used, the external clock input is
divided by the asynchronous ripple counter-type
prescaler so that the prescaler output is symmetrical.
For the external clock to meet the sampling
requirement, the ripple counter must be taken into
account. Therefore, it is necessary for T0CKI to have a
period of at least 4T

OSC (and a small RC delay of

40 ns) divided by the prescaler value. The only
requirement on T0CKI high and low time is that they
do not violate the minimum pulse width requirement of
10 ns. Refer to parameters 40, 41 and 42 in the
electrical specification of the desired device.

6.1.2 TIMER0 INCREMENT DELAY
Since the prescaler output is synchronized with the

internal clocks, there is a small delay from the time the
external clock edge occurs to the time the Timer0
module is actually incremented. Figure 6-5 shows the
delay from the external clock edge to the timer
incrementing.

FIGURE 6-5: TIMER0 TIMING WITH EXTERNAL CLOCK

Increment Timer0 (Q4)

External Clock Input or

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

Timer0

T0 T0 + 1 T0 + 2

Small pulse
misses sampling

External Clock/Prescaler
Output After Sampling

(3)

Note 1:

2:
3:

Delay from clock input change to Timer0 increment is 3Tosc to 7Tosc. (Duration of Q = Tosc).
Therefore, the error in measuring the interval between two edges on Timer0 input = ± 4Tosc max.
External clock if no prescaler selected, Prescaler output otherwise.
The arrows indicate the points in time where sampling occurs.

Prescaler Output (2)

(1)

PIC16CR54C

DS40191A-page 24 Preliminary  1998 Microchip Technology Inc.

6.2 Prescaler

An 8-bit counter is available as a prescaler for the
Timer0 module, or as a postscaler for the Watchdog
Timer (WDT) (WDT postscaler not implemented on
PIC16C52), respectively (Section 6.1.2). For simplicity,
this counter is being referred to as “prescaler”
throughout this data sheet. Note that the prescaler
may be used by either the Timer0 module or the WDT,
but not both. Thus, a prescaler assignment for the
Timer0 module means that there is no prescaler for
the WDT, and vice-versa.

The PSA and PS2:PS0 bits (OPTION<3:0>) determine
prescaler assignment and prescale ratio.

When assigned to the Timer0 module, all instructions
writing to the TMR0 register (e.g., CLRF 1, MOVWF 1,
BSF 1,x, etc.) will clear the prescaler. When assigned
to WDT, a CLRWDT instruction will clear the prescaler
along with the WDT. The prescaler is neither readable
nor writable. On a RESET, the prescaler contains all
'0's.

6.2.1 SWITCHING PRESCALER ASSIGNMENT
The prescaler assignment is fully under software control

(i.e., it can be changed “on the fly” during program
execution). To avoid an unintended device RESET, the

following instruction sequence (Example 6-1) must be
executed when changing the prescaler assignment from
Timer0 to the WDT.

EXAMPLE 6-1: CHANGING PRESCALER

(TIMER0→WDT)

1.CLRWDT ;Clear WDT

2.CLRF TMR0 ;Clear TMR0 & Prescaler

3.MOVLW '00xx1111’b ;These 3 lines (5, 6, 7)

4.OPTION ; are required only if
; desired

5.CLRWDT ;PS<2:0> are 000 or 001

6.MOVLW '00xx1xxx’b ;Set Postscaler to

7.OPTION ; desired WDT rate

To change prescaler from the WDT to the Timer0
module, use the sequence shown in Example 6-2. This
sequence must be used even if the WDT is disabled. A
CLRWDT instruction should be executed before switching
the prescaler.

EXAMPLE 6-2: CHANGING PRESCALER

(WDT→TIMER0)

CLRWDT ;Clear WDT and

;prescaler

MOVLW 'xxxx0xxx' ;Select TMR0, new

;prescale value and
;clock source

OPTION

FIGURE 6-6: BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER

T0CKI

T0SE

pin

TCY ( = Fosc/4)

Sync

2

Cycles

TMR0 reg

8-bit Prescaler

8 - to - 1MUX

M

MUX

Watchdog

Timer

PSA

0

1

0

1

WDT

Time-Out

PS2:PS0

8

Note: T0CS, T0SE, PSA, PS2:PS0 are bits in the OPTION register.

PSA

WDT Enable bit

0

1

0

1

Data Bus

8

PSA

T0CS

M
U

X

M

U
X

U
X

 1998 Microchip Technology Inc. Preliminary DS40191A-page 25

PIC16CR54C

7.0 SPECIAL FEATURES OF THE
CPU

What sets a microcontroller apart from other
processors are special circuits that deal with the
needs of real-time applications. The PIC16C5X family
of microcontrollers has a host of such features
intended to maximize system reliability, minimize cost
through elimination of external components, provide
power saving operating modes and offer code
protection. These features are:

• Oscillator selection

• Reset

• Power-On Reset (POR)

• Device Reset Timer (DRT)

• Watchdog Timer (WDT)

• SLEEP

• Code protection

The PIC16CR54C Family has a Watchdog Timer
which can be shut off only through configuration bit
WDTE. It runs off of its own RC oscillator for added
reliability. There is an 18 ms delay provided by the
Device Reset Timer (DRT), intended to keep the chip
in reset until the crystal oscillator is stable. With this
timer on-chip, most applications need no external
reset circuitry.

The SLEEP mode is designed to offer a very low
current power-down mode. The user can wak e up from
SLEEP through external reset or through a Watchdog
Timer time-out. Several oscillator options are also
made available to allow the par t to fit the application.
The RC oscillator option saves system cost while the
LP crystal option saves power. A set of configuration
bits are used to select various options.

7.1 Configuration Bits

Configuration bits can be programmed to select
various device configurations. Two bits are for the
selection of the oscillator type and one bit is the
Watchdog Timer enable bit. Nine bits are code
protection bits (Figure 7-1 and Figure 7-2) for the
PIC16CR54C devices.

ROM devices have the oscillator configuration
programmed at the factory and these parts are tested
accordingly (see "Product Identification System"
diagrams in the back of this data sheet).

FIGURE 7-1: CONFIGURATION WORD FOR PIC16CR54C

CP CP CP CP CP CP CP CP CP WDTE FOSC1 FOSC0 Register: CONFIG

Address

(1)

: 0FFFh

bit11 10 9 8 7 6 5 4 3 2 1 bit0

bit 11-3: CP: Code protection bits

1 = Code protection off
0 = Code protection on

bit 2: WDTE: Watchdog timer enable bit

1 = WDT enabled
0 = WDT disabled

bit 1-0: FOSC1:FOSC0: Oscillator selection bits

11 = RC oscillator
10 = HS oscillator
01 = XT oscillator
00 = LP oscillator

Note 1: Refer to the PIC16C5X Programming Specification (Literature number DS30190) to determine how to

access the configuration word.

PIC16CR54C

DS40191A-page 26 Preliminary  1998 Microchip Technology Inc.

7.2 Oscillator Configurations

7.2.1 OSCILLATOR TYPES

PIC16CR54Cs can be operated in four different
oscillator modes. The user can program two
configuration bits (FOSC1:FOSC0) to select one of
these four modes:

• LP: Low Power Crystal

• XT: Crystal/Resonator

• HS: High Speed Crystal/Resonator

• RC: Resistor/Capacitor

7.2.2 CRYSTAL OSCILLATOR / CERAMIC
RESONATORS

In XT, LP or HS modes, a crystal or ceramic resonator
is connected to the OSC1/CLKIN and OSC2/CLKOUT
pins to establish oscillation (Figure 7-2). The
PIC16CR54C oscillator design requires the use of a
parallel cut crystal. Use of a series cut crystal may
give a frequency out of the crystal manufacturers
specifications. When in XT, LP or HS modes, the
device can have an external clock source drive the
OSC1/CLKIN pin (Figure 7-3).

FIGURE 7-2: CRYSTAL OPERATION

(OR CERAMIC RESONATOR)
(HS, XT OR LP OSC
CONFIGURATION)

Note 1: See Capacitor Selection tables for

recommended values of C1 and C2.

2: A series resistor (RS) may be required for

AT strip cut crystals.

3: RF varies with the crystal chosen (approx.

value = 10 MΩ).

C1

(1)

C2

(1)

XTAL

OSC2

OSC1

RF

(3)

SLEEP

To internal

logic

RS

(2)

PIC16CR54C

FIGURE 7-3: EXTERNAL CLOCK INPUT

OPERATION (HS, XT OR LP
OSC CONFIGURATION)

TABLE 7-1: CAPACITOR SELECTION

FOR CERAMIC RESONATORS

- PIC16CR54C

TABLE 7-2: CAPACITOR SELECTION

FOR CRYSTAL OSCILLATOR

- PIC16CR54C

Osc

Type

Resonator

Freq

Cap. RangeC1Cap. Range

C2

XT 455 kHz

2.0 MHz

4.0 MHz

68-100 pF

15-33 pF
10-22 pF

68-100 pF

15-33 pF
10-22 pF

HS 8.0 MHz

16.0 MHz

10-22 pF

10 pF

10-22 pF

10 pF

These values are for design guidance only. Since
each resonator has its own characteristics, the user
should consult the resonator manufacturer for
appropriate values of external components.

Osc

Type

Resonator

Freq

Cap.Range

C1

Cap. Range

C2

LP 32 kHz

(1)

15 pF 15 pF

XT 100 kHz

200 kHz
455 kHz

1 MHz
2 MHz
4 MHz

15-30 pF
15-30 pF
15-30 pF
15-30 pF

15 pF
15 pF

200-300 pF
100-200 pF

15-100 pF

15-30 pF

15 pF
15 pF

HS 4 MHz

8 MHz

20 MHz

15 pF
15 pF
15 pF

15 pF
15 pF
15 pF

Note 1: For V

DD > 4.5V, C1 = C2 ≈ 30 pF is

recommended.
These values are for design guidance only. Rs may
be required in HS mode as well as XT mode to avoid
overdriving crystals with low drive lev el specifi cation.
Since each crystal has its own characteristics, the
user should consult the crystal manufacturer for
appropriate values of external components.

Note: If you change from this device to

another device, please verify oscillator
characteristics in your application.

Clock from
ext. system

OSC1

OSC2

PIC16CR54C

Open