Computer Hardware User's Guide

Subtract Reverse Integer With Borrow SUBRB
13-239 Assembly Language Instructions
Syntax SUBRB src, dst
Operation src – dst – C → dst
Operands src general addressing modes (G):
0 0 register (R n , 0 ≤ n ≤ 27)
0 1 direct
1 0 indirect (disp = 0–255, IR0, IR1)
1 1 immediate
dst register (R n , 0 ≤ n ≤ 27)
Opcode
31 2423 16 8 7 015
000 1 1 0
0 10
dst
G
src
Description The difference of the src, dst , and C operands is loaded into the dst register.
The dst and src operands are assumed to be signed integers.
Cycles 1
Status Bits These condition flags are modified only if the destination register is R7–R0.
LUF Unaffected
LV 1 if an integer overflow occurs; unchanged otherwise
UF 0
N 1 if a negative result is generated; 0 otherwise
Z 1 if a 0 result is generated; 0 otherwise
V 1 if an integer overflow occurs; 0 otherwise
C 1 if a borrow occurs; 0 otherwise
OVM Operation is affected by OVM bit value.
Example SUBRB R4,R6
Before Instruction After Instruction
R4 00 0000 03CB R4 00 0000 03CB
R6 00 0000 0258 R6 00 0000 0172
LUF 0 LUF 0
LV 0 LV 0
UF 0 UF 0
N 0 N 0
Z 0 Z 0
V 0 V 0
C 1 C 0
600
971
370
971
Mode Bit