Microchip Technology Inc PIC16C505T-20I-SL, PIC16C505-20E-SL, PIC16C505-20I-JW, PIC16C505-20I-P, PIC16C505-20I-SL Datasheet

PIC16C505

14-Pin, 8-Bit CMOS Microcontroller

Device included in this Data Sheet:

PIC16C505

High-Performance RISC CPU:

• Only 33 instructions to learn

• Operating speed:

- DC - 20 MHz clock input

- DC - 200 ns instruction cycle

Device

Program Data

Memory

PIC16C505 1024 x 12 72 x 8

• Direct, indirect and relative addressing modes for
data and instructions

• 12 bit wide instructions

• 8 bit wide data path

• 2-level deep hardware stack

• Eight special function hardware registers

• Direct, indirect and relative addressing modes for
data and instructions

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

Peripheral Features:

• 11 I/O pins with individual direction control

• 1 input pin

• High current sink/source for direct LED drive

• Timer0: 8-bit timer/counter with 8-bit
programmable prescaler

FIGURE 1: PIN DIAGRAM:

PDIP, SOIC, Ceramic Side Brazed

Special Microcontroller Features:

• In-Circuit Serial Programming (ICSP™)

• Power-on Reset (POR)

• Device Reset Timer (DRT)

• Watchdog Timer (WDT) with dedicated on-chip
RC oscillator for reliable operation

• Programmable Code Protection

• Internal weak pull-ups on I/O pins

• Wake-up from Sleep on pin change

• Power-saving Sleep mode

• Selectable oscillator options:

- INTRC: Precision internal 4 MHz oscillator

- EXTRC: External 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
technology

• Fully static design

• Wide operating voltage range (2.5V to 5.5V)

• Wide temperature ranges

- Commercial: 0˚C to +70˚C

- Industrial: -40˚C to +85˚C

- Extended: -40˚C to +125˚C

- < 1.0 µA typical standby current @ 5V

• Low power consumption

- < 2.0 mA @ 5V, 4 MHz

- 15 µA typical @ 3.0V, 32 kHz for TMR0 run-

ning in SLEEP mode

- < 1.0 µA typical standby current @ 5V

RB5/OSC1/CLKIN

RB4/OSC2/CLKOUT

RB3/MCLR/V

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1998 Microchip Technology Inc.

VDD

RC5/T0CKI

RC4
RC3

1

2

3

PP

4

5

6

7

14

PIC16C505

13

12

11

10

9

8

SS

V
RB0
RB1
RB2
RC0
RC1
RC2

Preliminary

DS40192A-page 1

PIC16C505

TABLE OF CONTENTS

1.0 General Description..................................................................................................................................................................... 3

2.0 PIC16C505 Device Varieties....................................................................................................................................................... 5

3.0 Architectural Overview ................................................................................................................................................................ 7

4.0 Memory Organization................................................................................................................................................................ 11

5.0 I/O Port...................................................................................................................................................................................... 19

6.0 Timer0 Module and TMR0 Register .......................................................................................................................................... 23

7.0 Special Features of the CPU..................................................................................................................................................... 27

8.0 Instruction Set Summary........................................................................................................................................................... 39

9.0 Development Support................................................................................................................................................................ 51

10.0 Electrical Characteristics - PIC16C505 ..................................................................................................................................... 55

11.0 DC and AC Characteristics - PIC16C505.................................................................................................................................. 65

12.0 Packaging Information............................................................................................................................................................... 69

INDEX.................................................................................................................................................................................................. 73

PIC16C505 Product Identification System........................................................................................................................................... 77

To Our Valued Customers

We constantly strive to improve the quality of all our products and documentation. We have spent an exceptional
amount of time to ensure that these documents are correct. However, we realize that we may have missed a few
things. If you find any information that is missing or appears in error, please use the reader response form in the
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DS40192A-page 2

Preliminary



1998 Microchip Technology Inc.

PIC16C505

1.0 GENERAL DESCRIPTION

The PIC16C505 from Microchip Technology is a low­cost, high performance, 8-bit, fully static, EPROM/
ROM-based CMOS microcontroller. It employs a RISC
architecture with only 33 single word/single cycle
instructions. All instructions are single cycle (1 µs)
except for program branches which take two cycles.
The PIC16C505 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 PIC16C505 product is equipped with special fea­tures 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 five oscillator configurations to choose from,
including INTRC internal oscillator mode and the
power-saving LP (Low Power) oscillator. Power saving
SLEEP mode, Watchdog Timer and code protection
features improve system cost, power and reliability.

The PIC16C505 is available in the cost-effective One­Time-Programmable (OTP) version, which is 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 PIC16C505 product is supported by a full-featured
macro assembler, a software simulator, an in-circuit
emulator, a ‘C’ compiler, 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 PIC16C505 fits perfectly in applications ranging
from personal care appliances and security systems to
low-power remote transmitters/receivers. The EPROM
technology makes customizing application programs
(transmitter codes, appliance settings, receiver fre­quencies, etc.) extremely fast and convenient. The
small footprint packages, for through hole or surface
mounting, make this microcontroller perfect for applica­tions with space limitations. Low-cost, low-power, high
performance, ease of use and I/O flexibility make the
PIC16C505 very versatile even in areas where no
microcontroller use has been considered before (e.g.,
timer functions, replacement of “glue” logic and PLD’s
in larger systems, coprocessor applications).

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1998 Microchip Technology Inc.

Preliminary

DS40192A-page 3

PIC16C505

TABLE 1-1: PIC16C505 DEVICE

PIC16C505

Clock

Memory

Peripherals

Features

The PIC16C505 device has Power-on Reset, selectable Watchdog Timer, selectable code protect,
high I/O current capability and precision internal oscillator.
The PIC16C505 device uses serial programming with data pin RB0 and clock pin RB1.

Maximum Frequency
of Operation (MHz)

EPROM Program Memory 1024
Data Memory (bytes) 72
Timer Module(s) TMR0
Wake-up from SLEEP on

pin change
I/O Pins 11
Input Pins 1
Internal Pull-ups Yes
In-Circuit Serial Programming Yes
Number of Instructions 33
Packages 14-pin DIP, SOIC, JW

20

Yes

DS40192A-page 4

Preliminary

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1998 Microchip Technology Inc.

PIC16C505

2.0 PIC16C505 DEVICE VARIETIES

A variety of 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 PIC16C505 Product
Identification System at the back of this data sheet to
specify the correct part number.

2.1 UV Erasab

The UV erasable version, offered in ceramic side
brazed package, is optimal for prototype development
and pilot programs.

The UV erasable version can be erased and
reprogrammed to any of the configuration modes.

Note:

Please note that erasing the device will
also erase the pre-programmed internal
calibration value for the inter nal oscillator.
The calibration value must be saved prior
to erasing the part.

Microchip's PICSTAR T
grammers all support programming of the PIC16C505.
Third party programmers also are available; refer to the

Microchip Third Party Guide

2.2 One-Time-Pr
Devices

The availability of OTP devices is especially useful for
customers who need the flexibility for frequent code
updates or small volume applications.

The OTP devices, pac kaged in plastic packages permit
the user to program them once. In addition to the
program memory, the configuration bits must also be
programmed.

le Devices



PLUS and PRO MATE pro-

for a list of sources.

ogrammable (OTP)

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 b ut with all EPROM locations and fuse
options already programmed by the factory. Certain
code and prototype verification procedures do apply
before production shipments are availab le. Please con­tact your local Microchip Technology sales office for
more details.

2.4 Serializ

Microchip offers a 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.

Serial programming allows each device to have a
unique number which can serve as an entry-code,
password or ID number.

ed Quick-Turnaround

Production (SQTP

SM

vices

) De

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1998 Microchip Technology Inc.

Preliminary

DS40192A-page 5

PIC16C505

NOTES:

DS40192A-page 6

Preliminary



1998 Microchip Technology Inc.

PIC16C505

3.0 ARCHITECTURAL OVERVIEW

The high performance of the PIC16C505 can be
attributed to a number of architectural features
commonly found in RISC microprocessors. To begin
with, the PIC16C505 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 PIC16C505 addresses 1K x 12 of program
memory. All program memory is internal.

The PIC16C505 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 PIC16C505 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 PIC16C505 simple yet efficient.
In addition, the learning curve is reduced significantly.

The PIC16C505 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
respectively, in subtraction. See the
instructions for examples.

A simplified block diagram is shown in Figure 3-1, with
the corresponding device pins described in Table 3-1.

ow and digit borrow out bit,

SUBWF

and

ADDWF

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1998 Microchip Technology Inc.

Preliminary

DS40192A-page 7

PIC16C505

FIGURE 3-1: PIC16C505 BLOCK DIAGRAM

12

Program Counter

STACK1
STACK2

Direct Addr

8

Device Reset

Timer

Power-on

Reset

Watchdog

Timer

Internal RC

OSC

5

OSC1/CLKIN

OSC2

Program

Bus

EPROM
1K x 12

Program

Memory

12

Instruction reg

Instruction

Decode &

Control

Timing

Generation

Data Bus

Registers

RAM Addr

Addr MUX

3

8

RAM

72 bytes

File

5-7

FSR reg

STATUS reg

MUX

ALU

W reg

Timer0

9

Indirect

Addr

8

PORTB

PORTC

RB0
RB1
RB2
RB3/MCLR/Vpp
RB4/OSC2/CLKOUT
RB5/OSC1/CLKIN

RC0
RC1
RC2
RC3
RC4
RC5/T0CKI

MCLR

Vdd, Vss

DS40192A-page 8

Preliminary



1998 Microchip Technology Inc.

PIC16C505

TABLE 3-1: PIC16C505 PINOUT DESCRIPTION

DIP

Name

RB0 13 13 I/O TTL/ST Bi-directional I/O port/ serial programming data. Can

RB1 12 12 I/O TTL/ST Bi-directional I/O port/ serial programming clock. Can

RB2 11 11 I/O TTL Bi-directional I/O port.
RC0 10 10 I/O TTL Bi-directional I/O port.
RC1 9 9 I/O TTL Bi-directional I/O port.
RC2 8 8 I/O TTL Bi-directional I/O port.
RC3 7 7 I/O TTL Bi-directional I/O port.
RC4 6 6 I/O TTL Bi-directional I/O port.
RC5/T0CKI 5 5 I/O ST Bi-directional I/O port. Can be configured as T0CKI.

/V

RB3/MCLR

RB4/OSC2/CLKOUT 3 3 I/O TTL Bi-directional I/O port/oscillator crystal output. Con-

RB5/OSC1/CLKIN 2 2 I/O TTL/ST Bidirectional IO port/oscillator crystal input/external

V

DD
SS

V

Legend: I = input, O = output, I/O = input/output, P = power, — = not used, TTL = TTL input,
ST = Schmitt Trigger input

PP

Pin #

SOIC
Pin #

4 4 I TTL Input port/master clear (reset) input/programming volt-

1 1 P — Positive supply for logic and I/O pins

14 14 P — Ground reference for logic and I/O pins

I/O/P
Type

Buffer

Type

be software programmed for internal weak pull-up and
wake-up from SLEEP on pin change. This buffer is a
Schmitt Trigger input when used in serial programming
mode.

be software programmed for internal weak pull-up and
wake-up from SLEEP on pin change. This buffer is a
Schmitt Trigger input when used in serial programming
mode.

age input. When configured as MCLR
active low reset to the device. Voltage on MCLR
must not exceed V
Can be software programmed for internal weak pull-up
and wake-up from SLEEP on pin change. Weak pull­up only when configured as RB3.

nections to crystal or resonator in crystal oscillator
mode (XT and LP modes only, RB4 in other modes).
Can be software programmed for internal weak pull-up
and wake-up from SLEEP on pin change. In EXTRC
and INTRC modes, the pin output can be configured to
CLKOUT, which has 1/4 the frequency of OSC1 and
denotes the instruction cycle rate.

clock source input (RB5 in Internal RC mode only,
OSC1 in all other oscillator modes). TTL input when
RB5, ST input in external RC oscillator mode.

Description

DD

during normal device operation.

, this pin is an

/V

PP

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1998 Microchip Technology Inc.

Preliminary

DS40192A-page 9

PIC16C505

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.

FIGURE 3-2: CLOCK/INSTRUCTION CYCLE

Q2 Q3 Q4

OSC1

Q1
Q2
Q3
Q4
PC

Q1

PC PC+1 PC+2

Fetch INST (PC)

Execute INST (PC-1) Fetch INST (PC+1)

Q1

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.,
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).

Q2 Q3 Q4

Execute INST (PC) Fetch INST (PC+2)

Q2 Q3 Q4

Q1

Execute INST (PC+1)

Internal
phase
clock

GOTO

)

EXAMPLE 3-1: INSTRUCTION PIPELINE FLOW

1. MOVLW 03H

2. MOVWF PORTB

3. CALL SUB_1

4. BSF PORTB, BIT1

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.

DS40192A-page 10

Fetch 1 Execute 1

Fetch 2 Execute 2

Preliminary

Fetch 3 Execute 3

Fetch 4 Flush

Fetch SUB_1 Execute SUB_1



1998 Microchip Technology Inc.

PIC16C505

4.0 MEMORY ORGANIZATION

PIC16C505 memory is organized into program mem­ory and data memory. For the PIC16C505, a paging
scheme is used. Program memory pages are accessed
using one STATUS register bit. Data memory banks
are accessed using the File Select Register (FSR).

4.1 Pr

The PIC16C505 devices have a 12-bit Program
Counter (PC).

The 1K x 12 (0000h-03FFh) for the PIC16C505 are
physically implemented. Refer to Figure 4-1.
Accessing a location above this boundary will cause a
wrap-around within the first 1K x 12 space. The
effective reset vector is at 0000h, (see Figure 4-1).
Location 03FFh (PIC16C505) contains the internal
clock oscillator calibration value. This value should
never be overwritten.

ogram Memory Organization

FIGURE 4-1: PROGRAM MEMORY MAP

AND STACK FOR THE
PIC16C505

CALL, RETLW

PC<11:0>

Stack Level 1
Stack Level 2

Reset Vector (note 1)

Space

User Memory

On-chip Program

Memory

1024 Word

Note 1: Address 0000h becomes the

effective reset vector. Location
03FFh (PIC16C505) contains the
MOVLW XX INTERNAL RC oscillator
calibration value.

12

0000h

01FFh
0200h

03FFh
0400h

7FFh

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1998 Microchip Technology Inc.

Preliminary

DS40192A-page 11

PIC16C505

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.

FIGURE 4-2: PIC16C505 REGISTER FILE MAP

FSR<6:5> 00 01

File Address

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

07h
08h

0Fh

10h

1Fh

Note 1: Not a physical register.

(1)

INDF

TMR0

PCL

STATUS

FSR

OSCCAL

PORTB
PORTC

General
Purpose
Registers

General
Purpose
Registers

Bank 0

20h

2Fh
30h

General
Purpose
Registers

3Fh

Bank 1

For the PIC16C505, the register file is composed of 8
special function registers, 24 general purpose
registers, and 48 general purpose registers that may
be addressed using a banking scheme (Figure 4-2).

4.2.1 GENERAL PURPOSE REGISTER FILE The general purpose register file is accessed either

directly or indirectly through the file select register
FSR (Section 4.8).

10

40h

Addresses map back to
addresses in Bank 0.

4Fh

50h

General
Purpose
Registers

5Fh

Bank 2

11

60h

6Fh

70h

General
Purpose
Registers

7Fh

Bank 3

DS40192A-page 12

Preliminary

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1998 Microchip Technology Inc.

PIC16C505

4.2.2 SPECIAL FUNCTION REGISTERS

The Special Function Registers (SFRs) 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.

TABLE 4-1: SPECIAL FUNCTION REGISTER (SFR) SUMMARY

Value on

Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

00h INDF Uses contents of FSR to address data memory (not a physical register)
01h TMR0 8-bit real-time clock/counter

(1)

02h
03h STATUS RBWUF
04h
05h OSCCAL CAL5 CAL4 CAL3 CAL2 CAL1 CAL0
N/A TRISB
N/A TRISC
N/A OPTION RBWU
06h PORTB
07h PORTC

Legend: Shaded cellls not used by Port Registers, read as ‘0’, — = unimplemented, read as ‘0’, x = unknown, u = unchanged.

PCL Low order 8 bits of PC

— PAO TO PD Z DC C

FSR

Indirect data memory address pointer

— — I/O control registers
— — I/O control registers

RBPU TOCS TOSE PSA PS2 PS1 PS0
— — RB5 RB4 RB3 RB2 RB1 RB0
— — RC5 RC4 RC3 RC2 RC1 RC0

— —

Power-On

Reset

xxxx xxxx uuuu uuuu uuuu uuuu
xxxx xxxx uuuu uuuu uuuu uuuu
1111 1111 1111 1111 1111 1111
0001 1xxx 000q quuu 100q quuu
110x xxxx 11uu uuuu 11uu uuuu
1000 00-- uuuu uu-- uuuu uu--

--11 1111 --11 1111 --11 1111

--11 1111 --11 1111 --11 1111
1111 1111 1111 1111 1111 1111

--xx xxxx --uu uuuu --uu uuuu

--xx xxxx --uu uuuu --uu uuuu

Value on

CLR and

M

WDT Reset

Value on
Wake-up on
Pin Change

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1998 Microchip Technology Inc.

Preliminary

DS40192A-page 13

PIC16C505

4.3 S

TATUS Register

This register contains the arithmetic status of the ALU,
the RESET status, and the page preselect bit.

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 T

O and PD bits are

For example,
bits and set the Z bit. This leaves the STATUS register
as

000u u1uu

It is recommended, therefore, that only
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
Instruction Set Summary.

not writable. Therefore, the result of an instruction with
the STATUS register as destination may be different
than intended.

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

RBWUF

bit7 6 5 4 3 2 1 bit0
bit 7: RBWUF: IO reset bit

bit 6: Unimplemented
bit 5: PA0: Program page preselect bits

bit 4: TO: Time-out bit

bit 3: PD: Power-down bit

bit 2: Z: Zero bit

bit 1: DC: Digit carry/borrow bit (for ADDWF and SUBWF instructions)

bit 0: C: Carry/borrow bit (for ADDWF, SUBWF and RRF, RLF instructions)

—

1 = Reset due to wake-up from SLEEP on pin change
0 = After power up or other reset

1 = Page 1 (200h - 3FFh)
0 = Page 0 (000h - 1FFh)
Each page is 512 bytes.
Using the PA0 bit as a general purpose read/write bit in devices which do not use it for program
page preselect is not recommended since this may affect upward compatibility with future products.

1 = After power-up, CLRWDT instruction, or SLEEP instruction
0 = A WDT time-out occurred

1 = After power-up or by the CLRWDT instruction
0 = By execution of the SLEEP instruction

1 = The result of an arithmetic or logic operation is zero
0 = The result of an arithmetic or logic operation is not zero

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

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

PA0 TO PD Z DC C R = Readable bit

CLRF STATUS

will clear the upper three

(where u = unchanged).

W = Writable bit

- n = Value at POR reset

BCF

, BSF and

DS40192A-page 14

Preliminary

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1998 Microchip Technology Inc.

PIC16C505

4.4 OPTION Register

The OPTION register is a 8-bit wide, write-only
register which contains various control bits to
configure the Timer0/WDT prescaler and Timer0.

Note: If TRIS bit is set to ‘0’, the wake-up on

change and pull-up functions are disabled
for that pin; i.e., note that TRIS overrides
OPTION control of RBPU

By executing the OPTION instruction, the contents of
the W register will be transferred to the OPTION
register. A RESET sets the OPTION<7:0> bits.

FIGURE 4-4: OPTION REGISTER

W-1 W-1 W-1 W-1 W-1 W-1 W-1 W-1

RBWU RBPU T0CS T0SE PSA PS2 PS1 PS0 W = Writable bit

bit7 6 5 4 3 2 1 bit0

bit 7: RBWU

bit 6: RBPU: Enable weak pull-ups (RB0, RB1, RB3, RB4)

bit 5: T0CS: Timer0 clock source select bit

bit 4: T0SE: Timer0 source edge select bit

bit 3: PSA: Prescaler assignment bit

bit 2-0: PS2:PS0: Prescaler rate select bits

: Enable wake-up on pin change (RB0, RB1, RB3, RB4)
1 = Disabled
0 = Enabled

1 = Disabled
0 = Enabled

1 = Transition on T0CKI pin
0 = Transition on internal instruction cycle clock, Fosc/4

1 = Increment on high to low transition on the T0CKI pin
0 = Increment on low to high transition on the T0CKI pin

1 = Prescaler assigned to the WDT
0 = Prescaler assigned to Timer0

Bit Value Timer0 Rate WDT Rate

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

U = Unimplemented bit

- n = Value at POR reset
Reference Table 4-1 for
other resets.

and RBWU.

 1998 Microchip Technology Inc. Preliminary DS40192A-page 15

PIC16C505

4.5 OSCCAL Register

The Oscillator Calibration (OSCCAL) register is used to
calibrate the internal 4 MHz oscillator. It contains six
bits for fine calibration.

FIGURE 4-5: OSCCAL REGISTER (ADDRESS 05h)PIC16C505

R/W-1 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 U-0 U-0
CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 — — R = Readable bit

bit7 bit0

bit 7-4: CAL<5:0>: Fine calibration

W = Writable bit
U = Unimplemented bit,

- n = Value at POR reset

read as ‘0’

DS40192A-page 16 Preliminary  1998 Microchip Technology Inc.

PIC16C505

4.6 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>. Bit 5 of the STATUS register
provides page information to bit 9 of the PC (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 4-6).

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 4-6: LOADING OF PC

BRANCH INSTRUCTIONS -

PIC16C505

GOTO Instruction

11

910

PC

8 7 0

PCL

4.6.1 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 oscillator calibration instruction. After
executing MOVLW XX, the PC will roll over to location
00h, and begin executing user code.

The STATUS register page preselect bits are cleared
upon a RESET, which means that page 0 is pre­selected.

Therefore, upon a RESET, a GOTO instruction will
automatically cause the program to jump to page 0
until the value of the page bits is altered.

4.7 Stack

PIC16C505 devices have a 12-bit wide hardware
push/pop stack.

push

A CALL instruction will
1 into stack 2 and then push the current program
counter value, incremented by one, into stac k level 1. If
more than two sequential CALL’s are executed, only
the most recent two return addresses are stored.

A RETLW instruction will
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.

the current value of stack

pop

the contents of stack level

Instruction Word

PA0

7 0

STATUS

CALL or Modify PCL Instruction

11

PC

 1998 Microchip Technology Inc. Preliminary DS40192A-page 17

8 7 0

910

Instruction Word

Reset to ‘0’

PA0

7 0

STATUS

PCL

PIC16C505

4.8 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 07 contains the value 10h

• Register file 08 contains the value 0Ah

• Load the value 07 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 = 08)

• 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.

FIGURE 4-7: DIRECT/INDIRECT ADDRESSING

Direct Addressing

(FSR)

6 5 4 (opcode) 0

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 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.

The device uses FSR6:5 to select between banks
0:3.

Indirect Addressing

6 5 4 (FSR) 0

bank select location select

Data
Memory(1)

00h

0Fh
10h

00 01 10 11

1Fh 3Fh 5Fh 7Fh

Bank 0 Bank 1 Bank 2 Bank 3

Addresses
map back to
addresses
in Bank 0.

bank location select

Note 1: For register map detail see Section 4.2.

DS40192A-page 18 Preliminary  1998 Microchip Technology Inc.

PIC16C505

5.0 I/O PORT

As with any other register, the I/O register can be
written and read under program control. However,
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 are all set.

5.1 PORTB

PORTB is an 8-bit I/O register. Only the low order 6
bits are used (RB5:RB0). Bits 7 and 6 are
unimplemented and read as '0's. Please note that RB3
is an input only pin. The configuration word can set
several I/O’s to alternate functions. When acting as
alternate functions the pins will read as ‘0’ during port
read. Pins RB0, RB1, RB3 and RB4 can be configured
with weak pull-ups and also with wake-up on change.
The wake-up on change and weak pull-up functions
are not pin selectable. If pin 4 is configured as MCLR
weak pull-up is always off and wake-up on change for
this pin is not enabled.

5.2 PORTC

PORTC is an 8-bit I/O register. Only the low order 6
bits are used (RC5:RC0). Bits 7 and 6 are unimple­mented and read as ‘0’s.

5.3 TRIS Registers

The output driver control register is 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
exceptions are RB3 which is input only and RC5 which
may be controlled by the option register, see Figure 4-

4.
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.

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 port pins, except RB3 which is input
only, may be used for both input and output
operations. For input operations these ports are non­latching. 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 TRIS must be
cleared (= 0). For use as an input, the corresponding
TRIS bit must be set. Any I/O pin (except RB3) can be
programmed individually as input or output.

FIGURE 5-1: EQUIVALENT CIRCUIT

FOR A SINGLE I/O PIN

Data
Bus

,

WR
Port

W
Reg

TRIS ‘f’

Note 1: I/O pins have protection diodes to VDD and VSS.

CK

TRIS
Latch

CK

Reset

Data
Latch

QD

VDD

Q

QD

Q

RD Port

P

N

VSS

I/O
pin

(1)

 1998 Microchip Technology Inc. Preliminary DS40192A-page 19

PIC16C505

TABLE 5-1: SUMMARY OF PORT REGISTERS

Value on

Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

N/A TRISB — — I/O control registers
N/A TRISC — — I/O control registers
N/A OPTION RBWU RBPU TOCS TOSE PSA PS2 PS1 PS0
03h STATUS RBWUF — PAO TO PD Z DC C
06h PORTB — — RB5 RB4 RB3 RB2 RB1 RB0
07h PORTC — — RC5 RC4 RC3 RC2 RC1 RC0

Legend: Shaded cellls not used by Port Registers, read as ‘0’, — = unimplemented, read as ‘0’, x = unknown, u = unchanged.

5.5 I/O Programming Considerations

EXAMPLE 5-1: READ-MODIFY-WRITE

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 bi­directional 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

;Initial PORTB Settings
; PORTB<5:3> Inputs
; PORTB<2:0> Outputs
;
; PORTB latch PORTB pins
; ---------- ---------­ BCF PORTB, 5 ;--01 -ppp --11 pppp
BCF PORTB, 4 ;--10 -ppp --11 pppp
MOVLW 007h ;
TRIS PORTB ;--10 -ppp --11 pppp
;
;Note that the user may have expected the pin
;values to be --00 pppp. The 2nd BCF caused
;RB5 to be latched as the pin value (High).

5.5.2 SUCCESSIVE OPERATIONS ON I/O

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 read­modify-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”, “wired­and”). The resulting high output currents may damage
the chip.

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

Power-On

Reset

--11 1111 --11 1111 --11 1111

--11 1111 --11 1111 --11 1111
1111 1111 1111 1111 1111 1111
0001 1xxx 000q quuu 100q quuu

--xx xxxx --uu uuuu --uu uuuu

--xx xxxx --uu uuuu --uu uuuu

INSTRUCTIONS ON AN
I/O PORT

PORTS

Value on

MCLR and

WDT Reset

Value on
Wake-up on
Pin Change

separate these instructions with a NOP or another
instruction not accessing this I/O port.

DS40192A-page 20 Preliminary  1998 Microchip Technology Inc.

FIGURE 5-2: SUCCESSIVE I/O OPERATION

PIC16C505

Instruction

fetched

RB5:RB0

Instruction

executed

Q4

Q3

Q1 Q2

PC PC + 1 PC + 2

MOVWF PORTB

Q1 Q2

MOVF PORTB,W

MOVWF PORTB

Q3

Port pin
written here

(Write to

PORTB)

Q4

Q3

Q1 Q2

NOP

Port pin
sampled here

MOVF PORTB,W

(Read

PORTB)

Q4

Q1 Q2

Q3

PC + 3

NOP

Q4

This example shows a write to PORTB
followed by a read from PORTB.

Data setup time = (0.25 TCY – TPD)
where: TCY = instruction cycle.

TPD = propagation delay

Therefore, at higher clock frequencies, a
write followed by a read may be problematic.

NOP

 1998 Microchip Technology Inc. Preliminary DS40192A-page 21

PIC16C505

NOTES:

DS40192A-page 22 Preliminary  1998 Microchip Technology Inc.

PIC16C505

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.

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 6-2 and Figure 6-3).
The user can work around this by writing an adjusted
value to the TMR0 register.

FIGURE 6-1: TIMER0 BLOCK DIAGRAM

RC5/T0CKI

Pin

T0SE

FOSC/4

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 6-5).

T0CS

0

1

(1)

Programmable

Prescaler

PS2, PS1, PS0

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
T0SE bit (OPTION<4>) determines the source edge.
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.

Data bus

PSout

1

0

(2)

3

(1)

PSA

(1)

Sync with

Internal

Clocks

(2 cycle delay)

PSout

Sync

8

TMR0 reg

 1998 Microchip Technology Inc. Preliminary DS40192A-page 23

PIC16C505

0

FIGURE 6-2: TIMER0 TIMING: INTERNAL CLOCK/NO PRESCALE

PC
(Program
Counter)

Instruction
Fetch

Timer0

Instruction
Executed

Q1 Q2 Q3 Q4

T0

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-1

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

MOVWF TMR0

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

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

FIGURE 6-3: TIMER0 TIMING: INTERNAL CLOCK/PRESCALE 1:2

PC
(Program
Counter)

Instruction
Fetch

Timer0

Instruction
Execute

Q1 Q2 Q3 Q4

T0 NT0+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

PC-1

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

MOVWF TMR0

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

T0+1

Write TMR0
executed

Read TMR0
reads NT0

NT0

Read TMR0
reads NT0

Read TMR0
reads NT0

Read TMR0
reads NT0

Read TMR0
reads NT0 + 1

TABLE 6-1: REGISTERS ASSOCIATED WITH TIMER0

Value on

Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

Power-On

Reset

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

RBWU RBPU T0CS T0SE PSA PS2 PS1 PS0 1111 1111 1111 1111
N/A TRISB I/O control registers --11 1111 --11 1111 --11 1111
N/A TRISC

Legend: Shaded cells not used by Timer0,

I/O control registers --11 1111 --11 1111 --11 1111

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

Value on

MCLR and

WDT Reset

Value on
Wake-up on
Pin Change

uuuu uuuu

1111 1111

T

DS40192A-page 24 Preliminary  1998 Microchip Technology Inc.