Datasheet

Instruction Set Description

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4.6.2.47 SUBC

SUBC[.W] Subtract source word with carry from destination word

SUBC.B Subtract source byte with carry from destination byte

Syntax

SUBC src,dst or SUBC.W src,dst

SUBC.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 done by adding

the 1s complement of the source + carry to the destination. The source operand is not

affected, the result is written to the destination operand. Used for 32, 48, and 64-bit

operands.

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 16-bit constant 7654h is subtracted from R5 with the carry from the previous

instruction. R5.19:16 = 0

SUBC.W #7654h,R5 ; Subtract 7654h + 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 points to the next 48-bit number afterwards. The

address R7 points to is in full memory range.

SUB @R5+,0(R7) ; Subtract LSBs. R5 + 2

SUBC @R5+,2(R7) ; Subtract MIDs with C. R5 + 2

SUBC @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. The address of CNT is in lower 64KB.

SUBC.B &CNT,0(R12) ; Subtract byte CNT from @R12

210

CPUX SLAU144J–December 2004–Revised July 2013

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