PIC18F1230/1330
2009 Microchip Technology Inc.
DS39758D-page 235
DECFSZ
Decrement f, Skip if 0
Syntax:
DECFSZ f {,d {,a}}
Operands:
0
f 255
d
[0,1]
a
[0,1]
Operation:
(f) – 1
dest,
skip if result = 0
Status Affected:
None
Encoding:
0010
11da
ffff
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’.
If the result is ‘0’, the next instruction,
which is already fetched, is discarded
and a NOP is executed instead, making
it a two-cycle instruction.
If ‘a(chǎn)’ is ‘0’, the Access Bank is selected.
If ‘a(chǎn)’ is ‘1’, the BSR is used to select the
GPR bank.
If ‘a(chǎn)’ is ‘0’ and the extended instruction
set is enabled, this instruction operates
in Indexed Literal Offset Addressing
mode whenever f
95 (5Fh). See
for details.
Words:
1
Cycles:
1(2)
Note:
3 cycles if skip and followed
by a 2-word instruction.
Q Cycle Activity:
Q1
Q2
Q3
Q4
Decode
Read
register ‘f’
Process
Data
Write to
destination
If skip:
Q1
Q2
Q3
Q4
No
operation
No
operation
No
operation
No
operation
If skip and followed by 2-word instruction:
Q1
Q2
Q3
Q4
No
operation
No
operation
No
operation
No
operation
No
operation
No
operation
No
operation
No
operation
Example:
HERE
DECFSZ
CNT, 1, 1
GOTO
LOOP
CONTINUE
Before Instruction
PC
=
Address (HERE)
After Instruction
CNT
=
CNT – 1
If CNT
=
0;
PC =
Address (CONTINUE)
If CNT
0;
PC =
Address (HERE + 2)
DCFSNZ
Decrement f, Skip if Not 0
Syntax:
DCFSNZ
f {,d {,a}}
Operands:
0
f 255
d
[0,1]
a
[0,1]
Operation:
(f) – 1
dest,
skip if result
0
Status Affected:
None
Encoding:
0100
11da
ffff
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’.
If the result is not ‘0’, the next
instruction, which is already fetched, is
discarded and a NOP is executed
instead, making it a two-cycle
instruction.
If ‘a(chǎn)’ is ‘0’, the Access Bank is selected.
If ‘a(chǎn)’ is ‘1’, the BSR is used to select the
GPR bank.
If ‘a(chǎn)’ is ‘0’ and the extended instruction
set is enabled, this instruction operates
in Indexed Literal Offset Addressing
mode whenever f
95 (5Fh). See
for details.
Words:
1
Cycles:
1(2)
Note:
3 cycles if skip and followed
by a 2-word instruction.
Q Cycle Activity:
Q1
Q2
Q3
Q4
Decode
Read
register ‘f’
Process
Data
Write to
destination
If skip:
Q1
Q2
Q3
Q4
No
operation
No
operation
No
operation
No
operation
If skip and followed by 2-word instruction:
Q1
Q2
Q3
Q4
No
operation
No
operation
No
operation
No
operation
No
operation
No
operation
No
operation
No
operation
Example:
HERE
DCFSNZ
TEMP, 1, 0
ZERO
:
NZERO
:
Before Instruction
TEMP
=
?
After Instruction
TEMP
=
TEMP – 1
If TEMP
=
0;
PC
=
Address (ZERO)
If TEMP
0;
PC
=
Address (NZERO)