PIC16F688
tion, or the destination designator ‘d’. A read operation
is performed on a register even if the instruction writes
to that register.
12.0 INSTRUCTION SET SUMMARY
The PIC16F688 instruction set is highly orthogonal and
is comprised of three basic categories:
For example, a CLRF GPIOinstruction 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.
• 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 12-1, while the various opcode
fields are summarized in Table 12-1.
TABLE 12-1: OPCODE FIELD
DESCRIPTIONS
Field
Description
f
W
b
k
x
Register file address (0x00 to 0x7F)
Working register (accumulator)
Table 12-2 lists the instructions recognized by the
MPASMTM assembler. A complete description of each
instruction is also available in the “PICmicro®
Mid-Range MCU Family Reference Manual”
(DS33023).
Bit address within an 8-bit file register
Literal field, constant data or label
Don’t care location (= 0or 1).
The assembler will generate code with x = 0.
It is the recommended form of use for
compatibility with all Microchip software tools.
For byte-oriented instructions, ‘f’ represents a file
register designator and ‘d’ represents a destination
designator. The file register designator specifies which
file register is to be used by the instruction.
d
Destination select; d = 0: store result in W,
d = 1: store result in file register f.
Default is d = 1.
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.
PC
TO
PD
Program Counter
Time-out bit
Power-down bit
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.
FIGURE 12-1:
GENERAL FORMAT FOR
INSTRUCTIONS
For literal and control operations, ‘k’ represents an
8-bit or 11-bit constant, or literal value.
Byte-oriented file register operations
13
8
7
6
0
OPCODE
d
f (FILE #)
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.
d = 0for destination W
d = 1for destination f
f = 7-bit file register address
Bit-oriented file register operations
13 10 9
b (BIT #)
7
6
0
OPCODE
f (FILE #)
Note: To maintain upward compatibility with
future products, do not use the OPTION
and TRISinstructions.
b = 3-bit bit address
f = 7-bit file register address
Literal and control operations
All instruction examples use the format ‘0xhh’ to
represent a hexadecimal number, where ‘h’ signifies a
hexadecimal digit.
General
13
8
7
0
0
OPCODE
k (literal)
12.1 READ-MODIFY-WRITE
OPERATIONS
k = 8-bit immediate value
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-
CALLand GOTOinstructions only
13 11 10
OPCODE
k = 11-bit immediate value
k (literal)
2004 Microchip Technology Inc.
Preliminary
DS41203B-page 119
MICROCHIP [ MICROCHIP ]
