PIC18F2420/2520/4420/4520
The literal instructions may use some of the following
operands:
24.0 INSTRUCTION SET SUMMARY
PIC18F2420/2520/4420/4520 devices incorporate the
standard set of 75 PIC18 core instructions, as well as an
extended set of 8 new instructions, for the optimization
of code that is recursive or that utilizes a software stack.
The extended set is discussed later in this section.
• A literal value to be loaded into a file register
(specified by ‘k’)
• The desired FSR register to load the literal value
into (specified by ‘f’)
• No operand required
(specified by ‘—’)
24.1 Standard Instruction Set
The control instructions may use some of the following
operands:
The standard PIC18 instruction set adds many
enhancements to the previous PIC® MCU instruction
sets, while maintaining an easy migration from these
PIC MCU instruction sets. Most instructions are a
single program memory word (16 bits), but there are
four instructions that require two program memory
locations.
• A program memory address (specified by ‘n’)
• The mode of the CALLor RETURNinstructions
(specified by ‘s’)
• The mode of the table read and table write
instructions (specified by ‘m’)
Each single-word instruction is a 16-bit word divided
into an opcode, which specifies the instruction type and
one or more operands, which further specify the
operation of the instruction.
• No operand required
(specified by ‘—’)
All instructions are a single word, except for four
double-word instructions. These instructions were
made double-word to contain the required information
in 32 bits. In the second word, the 4 MSbs are ‘1’s. If
this second word is executed as an instruction (by
itself), it will execute as a NOP.
The instruction set is highly orthogonal and is grouped
into four basic categories:
• Byte-oriented operations
• Bit-oriented operations
• Literal operations
All single-word instructions are executed in a single
instruction cycle, unless a conditional test is true or the
program counter is changed as a result of the instruc-
tion. In these cases, the execution takes two instruction
cycles, with the additional instruction cycle(s) executed
as a NOP.
• Control operations
The PIC18 instruction set summary in Table 24-2 lists
byte-oriented, bit-oriented, literal and control
operations. Table 24-1 shows the opcode field
descriptions.
The double-word instructions execute in two instruction
cycles.
Most byte-oriented instructions have three operands:
1. The file register (specified by ‘f’)
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.
Two-word branch instructions (if true) would take 3 μs.
2. The destination of the result (specified by ‘d’)
3. The accessed memory (specified by ‘a’)
The file register designator ‘f’ specifies which file
register is to be used by the instruction. The destination
designator ‘d’ specifies where the result of the opera-
tion is to be placed. If ‘d’ is zero, the result is placed in
the WREG register. If ‘d’ is one, the result is placed in
the file register specified in the instruction.
Figure 24-1 shows the general formats that the instruc-
tions can have. All examples use the convention ‘nnh’
to represent a hexadecimal number.
The Instruction Set Summary, shown in Table 24-2,
lists the standard instructions recognized by the
Microchip Assembler (MPASMTM).
All bit-oriented instructions have three operands:
1. The file register (specified by ‘f’)
2. The bit in the file register (specified by ‘b’)
3. The accessed memory (specified by ‘a’)
Section 24.1.1 “Standard Instruction Set” provides
a description of each instruction.
The bit field designator ‘b’ selects the number of the bit
affected by the operation, while the file register
designator ‘f’ represents the number of the file in which
the bit is located.
© 2008 Microchip Technology Inc.
DS39631E-page 267
MICROCHIP [ MICROCHIP ]
