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PIC17C7XX_13 Datasheet, PDF (211/306 Pages) Microchip Technology – High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D
PIC17C7XX
DECF
Syntax:
Operands:
Operation:
Status Affected:
Encoding:
Description:
Words:
Cycles:
Q Cycle Activity:
Q1
Decode
Decrement f
[ label ] DECF f,d
0  f  255
d  [0,1]
(f) – 1  (dest)
OV, C, DC, Z
0000 011d ffff ffff
Decrement register 'f'. If 'd' is 0, the
result is stored in WREG. If 'd' is 1, the
result is stored back in register 'f'.
1
1
Q2
Read
register 'f'
Q3
Process
Data
Q4
Write to
destination
Example:
DECF CNT, 1
Before Instruction
CNT = 0x01
Z
=0
After Instruction
CNT = 0x00
Z
=1
DECFSZ
Syntax:
Operands:
Operation:
Status Affected:
Encoding:
Description:
Words:
Cycles:
Q Cycle Activity:
Q1
Decode
Decrement f, skip if 0
[ label ] DECFSZ f,d
0  f  255
d  [0,1]
(f) – 1  (dest);
skip if result = 0
None
0001 011d ffff ffff
The contents of register 'f' are decre-
mented. If 'd' is 0, the result is placed in
WREG. 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.
1
1(2)
Q2
Read
register 'f'
Q3
Process
Data
Q4
Write to
destination
If skip:
Q1
No
operation
Q2
No
operation
Q3
No
operation
Q4
No
operation
Example:
HERE
NZERO
ZERO
DECFSZ
GOTO
Before Instruction
PC
= Address (HERE)
After Instruction
CNT =
If CNT =
PC =
If CNT 
PC =
CNT - 1
0;
Address (HERE)
0;
Address (NZERO)
CNT, 1
HERE
 1998-2013 Microchip Technology Inc.
DS30289C-page 211