PIC16F-ESLASHML datasheet(117/178 Pages) MICROCHIP

117 / 178 page

DS40044F-page 115

PIC16F627A/628A/648A

15.0

INSTRUCTION SET SUMMARY

Each PIC16F627A/628A/648A 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

PIC16F627A/628A/648A instruction set summary in

Table 15-2 lists byte-oriented, bit-oriented, and

literal and control operations. Table 15-1 shows the

opcode field descriptions.

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 number of the bit affected

by the operation, while ‘f’ represents the number 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.

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 for pins configured as inputs and

using the PORTB interrupt-on-change feature.

TABLE 15-1:

OPCODE FIELD

DESCRIPTIONS

The instruction set is highly orthogonal and is grouped

into three basic categories:

• Byte-oriented operations

• Bit-oriented operations

• Literal and control operations

All instructions

are executed within one single

instruction cycle, unless a conditional test is true or the

program counter is changed as a result of an

instruction. In this case, the execution takes two

instruction cycles with the second cycle executed as a

NOP

. One instruction cycle consists of four oscillator

periods. Thus, for an oscillator frequency of 4 MHz, the

normal instruction execution time is 1

μs. If a

conditional test is true or the program counter is

changed as a result of an instruction, the instruction

execution time is 2

μs.

Table 15-2 lists the instructions recognized by the

MPASM™ assembler.

Figure 15-1 shows the three general formats that the

instructions can have.

All examples use the following format to represent a

hexadecimal number:

0xhh

where ‘h’ signifies a hexadecimal digit.

FIGURE 15-1:

GENERAL FORMAT FOR

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

Time-out bit

Power-down bit

Note 1: Any unused opcode is reserved. Use of

any reserved opcode may cause unex-

pected operation.

2: To maintain upward compatibility with

future PIC MCU products, do not use the

OPTION

and TRIS instructions.

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

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

10 9

8 7

11 10

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