Datasheet

© 2008 Microchip Technology Inc. DS41249E-page 127
PIC16F785/HV785
17.0 INSTRUCTION SET SUMMARY
The PIC16F785/HV785 instruction set is highly orthog-
onal 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 format 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
MPASM
TM
assembler.
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.
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 always performed, even if the instruction is a Write
command.
For example, a CLRF PORTA instruction will read
PORTA, clear all the data bits, then write the result back
to PORTA. This example would have the unintended
result of clearing the condition that set the RAIF flag.
TABLE 17-1: OPCODE FIELD
DESCRIPTIONS
FIGURE 17-1: GENERAL FORMAT FOR
INSTRUCTIONS
Note: To maintain upward compatibility with
future products, do not use
the OPTION
and TRIS instructions.
Field Description
f
Register file address (0x00 to 0x7F)
W
Working register (accumulator)
b
Bit address within an 8-bit file register
k
Literal field, constant data or label
x
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.
d
Destination select; d = 0: store result in W,
d = 1: store result in file register f.
Default is d = 1.
PC
Program Counter
TO
Time-out bit
PD
Power-down bit
Byte-oriented file register operations
13 8 7 6 0
d = 0 for destination W
d = 1 for destination f
Bit-oriented file register operations
13 10 9 7 6 0
b = 3-bit bit address
f = 7-bit file register address
Literal and control operations
13 8 7 0
k = 8-bit immediate value
13 11 10 0
k = 11-bit immediate value
General
CALL and GOTO instructions only
OPCODE d f (FILE #)
f = 7-bit file register address
OPCODE b (BIT #) f (FILE #)
OPCODE k (literal)
OPCODE k (literal)