Conditional Subtract
SUBC
7-181
Assembly Language Instructions
SUBC affects OV but is not affected by OVM; therefore, the accumulator does
not saturate upon positive or negative overflows when executing this instruc-
tion. The carry bit is affected in the normal manner during this instruction: the
carry bit is cleared (C = 0) if the result of the subtraction generates a borrow
and is set (C = 1) if it does not generate a borrow.
Words
1
Cycles for a Single SUBC Instruction
Program
Operand
ROM
DARAM
SARAM
External
DARAM
1
1
1
1+p
SARAM
1
1
1, 2
†
1+p
External
1+d
1+d
1+d
2+d+p
† If the operand and the code are in the same SARAM block
Cycles for a Repeat (RPT) Execution of an SUBC Instruction
Program
Operand
ROM
DARAM
SARAM
External
DARAM
n
n
n
n+p
SARAM
n
n
n, n+1
†
n+p
External
n+nd
n+nd
n+nd
n+1+p+nd
† If the operand and the code are in the same SARAM block
Example 1
SUBC
DAT2
;(DP = 6)
Before Instruction
After Instruction
Data Memory
Data Memory
302h
01h
302h
01h
ACC
X
04h
ACC
0
08h
C
C
Example 2
RPT
#15
SUBC
*
Before Instruction
After Instruction
ARP
3
ARP
3
AR3
1000h
AR3
1000h
Data Memory
Data Memory
1000h
07h
1000h
07h
ACC
X
41h
ACC
1
20009h
C
C
Cycles
