Technical DB : Help on PIC's instructions.

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Introduction

This page on PIC 16F84 programming should help you to program your PIC more easily. It takes the most frequent combinations and translates them into one or more instructions for the PIC.
To do so, I use annotations inspired of more advanced languages :

W : the PIC accumulator.
a : a constant.
M,M1,M2 : addresses in RAM.

Caution : For some functions, I modify the value of the accumulator W.

If some points are not clear, if you miss some combinations or worse, if you find mistakes despite all we checked, please let us know by email, or in our forum.

The Pic 16F84

Assignment

W=0

CLRW

M=0

CLRF M

W=a

MOVLW a

M=a

W=a
M=W

MOVLW a
MOVWF M

M=W

MOVWF M

W=M

MOVF M,W

M1=M2

W=M2
M1=W

MOVF M2,W
MOVWF M1

Addition

W=W+1

ADDLW 1

M=W+1

W=W+1
M=W

ADDLW 1
MOVWF M

W=M+1

INCF M,W

M=M+1

INCF M,F

W=W+a

ADDLW a

M=W+a

W=W+a
M=W

ADDLW a
MOVWF M

W=M+a

W=a
W=W+M

MOVLW a
ADDWF M,W

M=M+a

W=a
M=W+M

MOVLW a
ADDWF M,F

W=W+M

ADDWF M,W

M=W+M

ADDWF M,F

W=M1+M2

W=M2
W=W+M1

MOVF M2,W
ADDWF M1,W

M1=M1+M2

W=M2
M1=W+M1

MOVF M2,W
ADDWF M1,F

Subtraction

W=-W

SUBLW 0

M=-W

W=-W
M=W

SUBLW 0
MOVWF M

W=-M

W=M
W=-W

MOVF M,W
SUBLW 0

M1=-M2

W=M2
W=-W
M1=W

MOVF M2,W
SUBLW 0
MOVWF M1

W=W-1

W=W+ (-1)

ADDLW 0xFF

M=W-1

W=W+ (-1)
M=W

ADDLW 0xFF
MOVWF M

W=M-1

DECF M,W

M=M-1

DECF M,F

W=W-a

W=W+ (-a)

ADDLW -a

M=W-a

W=W+ (-a)
M=W

ADDLW -a
MOVWF M

W=a-W

SUBLW a

M=a-W

W=a-W
M=W

SUBLW a
MOVWF M

W=M-a

W=a
W=M-W

MOVLW a
SUBWF M,W

M=M-a

W=a
M=M-W

MOVLW a
SUBWF M,F

W=a-M

W=M
W=a-W

MOVF M,W
SUBLW a

M=a-M

W=M
W=a-W
M=W

MOVF M,W
SUBLW a
MOVWF M

W=W-M

W=M-W
W=-W

SUBWF M,W
SUBLW 0

M=W-M

W=M-W
W=-W
M=W

SUBWF M,W
SUBLW 0
MOVWF M

W=M-W

SUBWF M,W

M=M-W

SUBWF M,F

W=M1-M2

W=M2
W=M1-W

MOVF M2,W
SUBWF M1,W

M1=M1-M2

W=M2
M1=M1-W

MOVF M2,W
SUBWF M1,F

M2=M1-M2

W=M2
W=M1-W
M2=W

MOVF M2,W
SUBWF M1,W
MOVWF M2

Logical Operation OR

W=W OR a

IORLW a

Truth table of OR function :

E1	E2	S
0	0	0
0	1	1
1	0	1
1	1	1

It is also used to change bits to 1.
if E2=1 then S always equals 1
if E2=0 then S is unchanged.

M=W OR a

W=W OR a
M=W

IORLW a
MOVWF M

W=M OR a

W=M
W=W OR a

MOVF M,W
IORLW a

M=M OR a

W=a
M=M OR W

MOVLW a
IORWF M,F

W=W OR M

IORWF M,W

M=W OR M

IORWF M,F

W=M1 OR M2

W=M2
W=W OR M1

MOVF M2,W
IORWF M1,W

M1=M1 OR M2

W=M2
M1=W OR M1

MOVF M2,W
IORWF M1,F

Logical Operation AND

W=W AND a

ANDLW a

Truth table of AND function :

E1	E2	S
0	0	0
0	1	0
1	0	0
1	1	1

It is also used to change bits to 0.
if E2=0 then S always equals 0
if E2=1 then S is unchanged.

M=W AND a

W=W AND a
M=W

ANDLW a
MOVWF M

W=M AND a

W=M
W=W AND a

MOVF M,W
ANDLW a

M=M AND a

W=a
M=M AND W

MOVLW a
ANDWF M,F

W=W AND M

ANDWF M,W

M=W AND M

ANDWF M,F

W=M1 AND M2

W=M2
W=W AND M1

MOVF M2,W
ANDWF M1,W

M1=M1 AND M2

W=M2
M1=W AND M1

MOVF M2,W
ANDWF M1,F

Logical Operation Exclusive OR ( XOR )

W=W XOR a

XORLW a

Truth table of XOR function :

E1	E2	S
0	0	0
0	1	1
1	0	0
1	1	1

It is also used to permute bits.
if E2=1 then S=NOT S
if E2=0 then S is unchanged.

M=W XOR a

W=W XOR a
M=W

XORLW a
MOVWF M

W=M XOR a

W=M
W=W XOR a

MOVF M,W
XORLW a

M=M XOR a

W=a
M=M XOR W

MOVLW a
XORWF M,F

W=W XOR M

XORWF M,W

M=W XOR M

XORWF M,F

W=M1 XOR M2

W=M2
W=W XOR M1

MOVF M2,W
XORWF M1,W

M1=M1 XOR M2

W=M2
M1=W XOR M1

MOVF M2,W
XORWF M1,F

Logical Operation NOT

W=NOT W

XORLW 0xFF

Truth table of NOT function :

E		S
0		1
1		0

It is also used to permute bits.

M=NOT W

W=NOT W
M=W

XORLW 0xFF
MOVWF M

W=NOT M

COMF M,W

M=NOT M

COMF M,F

M1=NOT M2

W=NOT M2
M1=W

COMF M,W
MOVWF M1

Bits assignement with b the bit number from 0 to 7

W(b)=0

ANDLW B'11111111'
with bit b equals 0

If you have to modify many bits it is better to use to OR or AND functions.

M(b)=0

BCF M,b

W(b)=1

IORLW B'00000000'
with bit b equals 1

M(b)=1

BSF M,b

Jump

Jump to a Label

GOTO Label

Call of the function Label

CALL Label

Returns of a function

RETURN

Returns of the result of a function

W=a
RETURN

RETLW a

Conditionnal jump

Note : To simplify the table, when the condition is true, a jump is made ( GOTO ) but you can replace it by a function call ( CALL ) or by a line of code and only one.

if M(b) = 1 goto Label

BTFSC M,b
GOTO Label

if M(b) = 0 goto Label

BTFSS M,b
GOTO Label

M=M-1
if M <> 0 goto Label

DECFSZ M,F
GOTO Label

W=M-1
if W <> 0 goto Label

DECFSZ M,W
GOTO Label

M=M+1
if M <> 256 goto Label

INCFSZ M,F
GOTO Label

W=M+1
if M <> 256 goto Label

INCFSZ M,W
GOTO Label

Res represents the result of the last instruction.

if Res = 0 goto Label

BTFSC STATUS,Z
GOTO Label

if Res <> 0 goto Label

BTFSS STATUS,Z
GOTO Label

After the SUBWF or SUBLW instruction, you can test :

if Res < 0 goto Label

BTFSS STATUS,C
GOTO Label

if Res >= 0 goto Label

BTFSC STATUS,C
GOTO Label

After the ADDWF or ADDLW instructions, you can test :

if Res > 255 goto Label

BTFSC STATUS,C
GOTO Label

if Res <= 255 goto Label

BTFSS STATUS,C
GOTO Label

Other frequent cases ( To jump when the condition is false : replace BTFSC by BTFSS )

if W = 0 goto Label

W = W + 0
if Res = 0 goto Label

ADDLW 0
BTFSC STATUS,Z
GOTO Label

if M = 0 goto Label

W=M
if Res = 0 goto Label

MOVF M,W
BTFSC STATUS,Z
GOTO Label

if W = a goto Label

W = a - W
if Res = 0 goto Label

SUBLW a
BTFSC STATUS,Z
GOTO Label

if M = a goto Label

W = a
W = M - W
if Res = 0 goto Label

MOVLW a
SUBWF M,W
BTFSC STATUS,Z
GOTO Label

if W = M goto Label

W = M - W
if Res = 0 goto Label

SUBWF M,W
BTFSC STATUS,Z
GOTO Label

if M1 = M2 goto Label

W = M2
W = M1 - W
if Res = 0 goto Label

MOVF M2,W
SUBWF M1,W
BTFSC STATUS,Z
GOTO Label

if M < 0 goto Label

BTFSC M,7
GOTO Label

if M >= 128 goto Label

BTFSC M,7
GOTO Label

if W <= a goto Label

W = a - W
if Res >= 0 goto Label

SUBLW a
BTFSC STATUS,C
GOTO Label

if M >= a goto Label

W = a
W = M - W
if Res >= 0 goto Label

MOVLW a
SUBWF M,W
BTFSC STATUS,C
GOTO Label

if W <= M goto Label

W = M - W
if Res >= 0 goto Label

SUBWF M,W
BTFSC STATUS,C
GOTO Label

if M1 >= M2 goto Label

W = M2
W = M1 - W
if Res >= 0 goto Label

MOVF M2,W
SUBWF M1,W
BTFSC STATUS,C
GOTO Label

Other functions

Right rotation with carry

RLF M,W
or RLF M,F

Left rotation with carry

RRF M,W
or RRF M,F

No opération

NOP

Permutation

SWAPF M,W
or SWAPF M,F

Clear Watchdog

CLRWDT

Sleep mode

SLEEP

Last modified : 8 feb 2000