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2005 Microchip Technology Inc.

Preliminary

DS41265A-page 213

PIC16F946

17.0

INSTRUCTION SET SUMMARY

The PIC16F946 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 17-1, while the various opcode

fields are summarized in Table 17-1.

Table 17-2 lists the instructions recognized by the

MPASMTM assembler. A complete description of each

instruction

also

available

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

operation, while ‘f’ represents the address of the file in

which the bit is located.

For literal and control operations, ‘k’ represents an

8-bit or 11-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

μs. 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.

17.1

READ-MODIFY-WRITE

OPERATIONS

Any instruction that specifies a file register as part of

the instruction performs a Read-Modify-Write (RMW)

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 GPIO instruction will read GPIO,

clear all the data bits, then write the result back to

GPIO. This example would have the unintended result

of clearing the condition that set the GPIF flag.

TABLE 17-1:

OPCODE FIELD

DESCRIPTIONS

Note:

To maintain upward compatibility with

future 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

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