Datasheet

PIC18F2220/2320/4220/4320
DS39599G-page 294 © 2007 Microchip Technology Inc.
SUBWFB Subtract W from f with Borrow
Syntax:
[ label ] SUBWFB f [,d [,a]]
Operands: 0 ≤ f ≤ 255
d ∈ [0,1]
a ∈ [0,1]
Operation: (f) – (W) – (C
) → dest
Status Affected: N, OV, C, DC, Z
Encoding:
0101 10da ffff ffff
Description: Subtract W and the Carry flag (bor-
row) from register ‘f’ (2’s complement
method). If ‘d’ is ‘0’, the result is
stored in W. If ‘d’ is ‘1’, the result is
stored back in register ‘f’ (default). If
‘a’ is ‘0’, the Access Bank will be
selected, overriding the BSR value. If
‘a’ is ‘1’, then the bank will be
selected as per the BSR value
(default).
Words: 1
Cycles: 1
Q Cycle Activity:
Q1 Q2 Q3 Q4
Decode Read
register ‘f’
Process
Data
Write to
destination
Example 1:
SUBWFB REG, 1, 0
Before Instruction
REG = 0x19 (0001 1001)
W = 0x0D (0000 1101)
C = 0x01
After Instruction
REG = 0x0C (0000 1011)
W = 0x0D (0000 1101)
C = 0x01
Z = 0x00
N = 0x00 ; result is positive
Example 2:
SUBWFB REG, 0, 0
Before Instruction
REG = 0x1B (0001 1011)
W = 0x1A (0001 1010)
C = 0x00
After Instruction
REG = 0x1B (0001 1011)
W = 0x00
C = 0x01
Z = 0x01 ; result is zero
N = 0x00
Example 3:
SUBWFB REG, 1, 0
Before Instruction
REG = 0x03 (0000 0011)
W = 0x0E (0000 1101)
C = 0x01
After Instruction
REG = 0xF5 (1111 0100)
; [2’s comp]
W = 0x0E (0000 1101)
C = 0x00
Z = 0x00
N = 0x01 ; result is negative