PIC18F010T-I/SN View Datasheet(PDF) - Microchip Technology
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'PIC18F010T-I/SN' PDF : 176 Pages View PDF
PIC18F010/020
4.7 Instructions in Program Memory
The program memory is addressed in bytes. Instruc-
tions are stored as two bytes or four bytes in program
memory. The least significant byte of an instruction
word is always stored in a program memory location
with an even address (LSB = ’0’). Figure 4-5 shows an
example of how instruction words are stored in the pro-
gram memory. To maintain alignment with instruction
boundaries, the PC increments in steps of 2 and the
LSB will always read ’0’ (see Section 4.4).
The CALL and GOTO instructions have an absolute pro-
gram memory address embedded into the instruction.
Since instructions are always stored on word bound-
aries, the data contained in the instruction is a word
address. The word address is written to PC<20:1>,
which accesses the desired byte address in program
memory. Instruction #2 in Figure 4-5 shows how the
instruction "GOTO 000006h’ is encoded in the program
memory. Program branch instructions, which encode a
relative address offset, operate in the same manner.
The offset value stored in a branch instruction repre-
sents the number of single word instructions that the
PC will be offset by. Section 13.0 provides further
details of the instruction set.
FIGURE 4-5:
INSTRUCTIONS IN PROGRAM MEMORY
Program Memory
Byte Locations
→
LSB = 1
Instruction 1: MOVLW
055h
0Fh
Instruction 2: GOTO
000006h
EFh
F0h
Instruction 3: MOVFF
123h, 456h
C1h
F4h
LSB = 0
55h
03h
00h
23h
56h
Word Address
↓
000000h
000002h
000004h
000006h
000008h
00000Ah
00000Ch
00000Eh
000010h
000012h
000014h
2001 Microchip Technology Inc.
Preliminary
DS41142A-page 29
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