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2003 Microchip Technology Inc.

DS39582B-page 159

PIC16F87XA

15.0

INSTRUCTION SET SUMMARY

The PIC16 instruction set is highly orthogonal and is

comprised of three basic categories:

Byte-oriented operations

Bit-oriented operations

Literal and control operations

Each PIC16 instruction is a 14-bit word divided into an

opcode which specifies the instruction type and one or

more operands which further specify the operation of

the instruction. The formats for each of the categories

is presented in Figure 15-1, while the various opcode

fields are summarized in Table 15-1.

Table 15-2 lists the instructions recognized by the

MPASM Assembler. A complete description of each

instruction is also available in the PICmicro Mid-Range

MCU Family Reference Manual (DS33023).

For byte-oriented instructions, ‘f’ represents a file

designator. The file register designator specifies which

file register is to be used by the instruction.

The destination designator specifies where the result of

the operation is to be placed. If ‘d’ is zero, the result is

placed in the W register. If ‘d’ is one, the result is placed

in the file register specified in the instruction.

For bit-oriented instructions, ‘b’ represents a bit field

designator which selects the bit affected by the opera-

tion, while ‘f’ represents the address of the file in which

the bit is located.

For literal and control operations, ‘k’ represents an

eight or eleven-bit constant or literal value

One instruction cycle consists of four oscillator periods;

for an oscillator frequency of 4 MHz, this gives a normal

instruction execution time of 1

s. All instructions are

executed within a single instruction cycle, unless a

conditional test is true, or the program counter is

changed as a result of an instruction. When this occurs,

the execution takes two instruction cycles with the

second cycle executed as a NOP.

All instruction examples use the format ‘0xhh’ to

represent a hexadecimal number, where ‘h’ signifies a

hexadecimal digit.

15.1

READ-MODIFY-WRITE

OPERATIONS

Any instruction that specifies a file register as part of

the instruction performs a Read-Modify-Write (R-M-W)

operation. The register is read, the data is modified,

and the result is stored according to either the instruc-

tion or the destination designator ‘d’. A read operation

is performed on a register even if the instruction writes

to that register.

For example, a “CLRF

PORTB

” instruction will read

PORTB, clear all the data bits, then write the result

back to PORTB. This example would have the unin-

tended result that the condition that sets the RBIF flag

would be cleared.

TABLE 15-1:

OPCODE FIELD

DESCRIPTIONS

FIGURE 15-1:

GENERAL FORMAT FOR

INSTRUCTIONS

Note:

To maintain upward compatibility with

future PIC16F87XA products, do not use

the OPTION and TRIS instructions.

Field

Description

Working register (accumulator)

Bit address within an 8-bit file register

Literal field, constant data or label

Don't care location (= 0 or 1).

The assembler will generate code with x = 0.

It is the recommended form of use for

compatibility with all Microchip software tools.

Destination select; d = 0: store result in W,

d = 1: store result in file register f.

Default is d = 1.

Program Counter

Time-out bit

Power-down bit

Byte-oriented file register operations

d = 0 for destination W

OPCODE

f (FILE #)

d = 1 for destination f

f = 7-bit file register address

Bit-oriented file register operations

10 9

7 6

OPCODE

b (BIT #)

f (FILE #)

b = 3-bit bit address

f = 7-bit file register address

Literal and control operations

OPCODE

k (literal)

k = 8-bit immediate value

OPCODE

k (literal)

k = 11-bit immediate value

General

CALL

and GOTO instructions only

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