PIC18F2331/2431/4331/4431
DECFSZ
Decrement f, Skip if 0
DCFSNZ
Decrement f, Skip if Not 0
Syntax:
[ label ] DECFSZ f [,d [,a]]
Syntax:
[ label ] DCFSNZ f [,d [,a]]
Operands:
0 f 255
d [0,1]
a [0,1]
Operands:
0 f 255
d [0,1]
a [0,1]
Operation:
(f) – 1 dest,
Operation:
(f) – 1 dest,
skip if result = 0
skip if result 0
Status Affected:
Encoding:
None
Status Affected:
Encoding:
None
0010
11da
ffff
ffff
0100
11da
ffff
ffff
Description:
The contents of register, ‘f’, are
Description:
The contents of register, ‘f’, are
decremented. If ‘d’ is ‘0’, the result is
placed in W. If ‘d’ is ‘1’, the result is
placed back in register, ‘f’.
decremented. If ‘d’ is ‘0’, the result is
placed in W. If ‘d’ is ‘1’, the result is
placed back in register, ‘f’.
If the result is ‘0’, the next instruction,
which is already fetched, is discarded,
and a NOPis executed instead, making
it a two-cycle instruction. If ‘a’ is ‘0’, the
Access Bank will be selected,
overriding the BSR value. If ‘a’ = 1,
then the bank will be selected as per
the BSR value.
If the result is not ‘0’, the next
instruction, which is already fetched, is
discarded, and a NOPis executed
instead, making it a two-cycle
instruction. If ‘a’ is ‘0’, the Access Bank
will be selected, overriding the BSR
value. If ‘a’ = 1, then the bank will be
selected as per the BSR value.
Words:
Cycles:
1
Words:
Cycles:
1
1(2)
1(2)
Note: 3 cycles if skip and followed
by a 2-word instruction.
Note: 3 cycles if skip and followed
by a 2-word instruction.
Q Cycle Activity:
Q1
Q Cycle Activity:
Q1
Q2
Q3
Q4
Q2
Q3
Q4
Decode
Read
register ‘f’
Process
Data
Write to
destination
Decode
Read
register ‘f’
Process
Data
Write to
destination
If skip:
Q1
If skip:
Q1
Q2
Q3
Q4
Q2
Q3
Q4
No
No
No
No
No
No
No
No
operation
operation
operation
operation
operation
operation
operation
operation
If skip and followed by 2-word instruction:
If skip and followed by 2-word instruction:
Q1
Q2
Q3
Q4
Q1
Q2
Q3
Q4
No
No
No
No
No
No
No
No
operation
operation
operation
operation
operation
operation
operation
operation
No
No
No
No
No
No
No
No
operation
operation
operation
operation
operation
operation
operation
operation
Example:
HERE
DECFSZ
GOTO
CNT
LOOP
Example:
HERE
ZERO
NZERO
DCFSNZ TEMP
:
:
CONTINUE
Before Instruction
PC
After Instruction
Before Instruction
TEMP
=
Address (HERE)
=
?
After Instruction
TEMP
CNT
=
CNT – 1
0;
Address (CONTINUE)
0;
=
=
=
=
TEMP – 1,
0;
Address (ZERO)
0;
If CNT
=
=
=
If TEMP
PC
If TEMP
PC
PC
If CNT
PC
Address (HERE + 2)
Address (NZERO)
2010 Microchip Technology Inc.
DS39616D-page 303
MICROCHIP [ MICROCHIP ]
