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Instruction Set Description
4.6.3.33 SUBCX
SUBCX.A
Subtract source address-word with carry from destination address-word
SUBCX.[W]
Subtract source word with carry from destination word
SUBCX.B
Subtract source byte with carry from destination byte
SUBCX.A src,dst
Syntax
SUBCX src,dst
or
SUBCX.W src,dst
SUBCX.B src,dst
Operation
(.not. src) + C + dst
→
dst or dst – (src – 1) + C
→
dst
Description
The source operand is subtracted from the destination operand. This is made by adding
the 1s complement of the carry to the destination. The source operand is not
affected, the result is written to the destination operand. Both operands may be located
in the full address space.
Status Bits
N:
Set if result is negative (MSB = 1), reset if positive (MSB = 0)
Z:
Set if result is zero, reset otherwise
C:
Set if there is a carry from the MSB, reset otherwise
V:
Set if the subtraction of a negative source operand from a positive destination
operand delivers a negative result, or if the subtraction of a positive source operand
from a negative destination operand delivers a positive result, reset otherwise (no
overflow).
Mode Bits
OSCOFF, CPUOFF, and GIE are not affected.
Example
A 20-bit constant 87654h is subtracted from R5 with the carry from the previous
instruction.
SUBCX.A
#87654h,R5
; Subtract C from R5
Example
A 48-bit number (3 words) pointed to by R5 (20-bit address) is subtracted from a 48-bit
counter in RAM, pointed to by R7. R5 auto-increments to point to the next 48-bit number.
SUBX.W
@R5+,0(R7)
; Subtract LSBs. R5 + 2
SUBCX.W
@R5+,2(R7)
; Subtract MIDs with C. R5 + 2
SUBCX.W
@R5+,4(R7)
; Subtract MSBs with C. R5 + 2
Example
Byte CNT is subtracted from the byte R12 points to. The carry of the previous instruction
is used. 20-bit addresses.
SUBCX.B
&CNT,0(R12)
; Subtract byte CNT from @R12
222
CPUX
SLAU272C – May 2011 – Revised November 2013
Copyright © 2011–2013, Texas Instruments Incorporated