PIC18F2331/2431/4331/4431
SUBWFB
Syntax:
Subtract W from f with Borrow
SWAPF
Swap f
Syntax:
[ label ] SWAPF f [,d [,a]]
[ label ] SUBWFB 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<3:0>) dest<7:4>,
(f<7:4>) dest<3:0>
Operation:
(f) – (W) – (C) dest
Status Affected:
Encoding:
N, OV, C, DC, Z
Status Affected:
Encoding:
None
0101
10da
ffff
ffff
0011
10da
ffff
ffff
Description:
Subtract W and the Carry flag (borrow)
from register, ‘f’ (2’s complement
Description:
The upper and lower nibbles of register,
‘f’, are exchanged. If ‘d’ is ‘0’, the result
is placed in W. If ‘d’ is ‘1’, the result is
placed in register, ‘f’. If ‘a’ is ‘0’, the
Access Bank will be selected, overrid-
ing the BSR value. If ‘a’ is ‘1’, then the
bank will be selected as per the BSR
value.
method). If ‘d’ is ‘0’, the result is stored in
W. If ‘d’ is ‘1’, the result is stored back in
register, ‘f’. 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.
Words:
Cycles:
1
1
Words:
Cycles:
1
1
Q Cycle Activity:
Q1
Q Cycle Activity:
Q1
Q2
Q3
Q4
Q2
Q3
Q4
Decode
Read
register ‘f’
Process
Data
Write to
Decode
Read
register ‘f’
Process
Data
Write to
destination
destination
Example 1:
SUBWFB REG, 1, 0
Before Instruction
Example:
SWAPF
REG
REG
W
C
=
=
=
0x19
0x0D
0x01
(0001 1001)
(0000 1101)
Before Instruction
REG
=
0x53
0x35
After Instruction
After Instruction
REG
=
REG
W
C
Z
N
=
0x0C
0x0D
0x01
0x00
0x00
(0000 1011)
(0000 1101)
=
=
=
=
; result is positive
Example 2:
SUBWFB REG, 0, 0
Before Instruction
REG
W
C
=
=
=
0x1B
0x1A
0x00
(0001 1011)
(0001 1010)
(0001 1011)
; result is zero
After Instruction
REG
W
C
Z
N
=
0x1B
0x00
0x01
0x01
0x00
=
=
=
=
Example 3:
Before Instruction
SUBWFB REG, 1, 0
REG
W
C
=
=
=
0x03
0x0E
0x01
(0000 0011)
(0000 1101)
After Instruction
REG
=
0xF5
(1111 0100)
; [2’s comp]
W
C
Z
=
=
=
=
0x0E
0x00
0x00
0x01
(0000 1101)
N
; result is negative
DS39616D-page 320
2010 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
