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Instruction Set Description
4.6.4.5
CMPA
CMPA
Compare the 20-bit source with a 20-bit destination register
CMPA Rsrc,Rdst
Syntax
CMPA #imm20,Rdst
Operation
(.not. src) + 1 + Rdst or Rdst – src
Description
The 20-bit source operand is subtracted from the 20-bit destination CPU register. This
is made by adding the 1s complement of the 1 to the destination register. The
result affects only the status bits.
Status Bits
N:
Set if result is negative (src > dst), reset if positive (src
≤
dst)
Z:
Set if result is zero (src = dst), reset otherwise (src
≠
dst)
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 immediate operand and R6 are compared. If they are equal, the program
continues at label EQUAL.
CMPA
#12345h,R6
; Compare R6 with 12345h
JEQ
EQUAL
; R6 = 12345h
...
; Not equal
Example
The 20-bit values in R5 and R6 are compared. If R5 is greater than (signed) or equal to
R6, the program continues at label GRE.
CMPA
R6,R5
; Compare R6 with R5 (R5 - R6)
JGE
GRE
; R5 >= R6
...
; R5 < R6
235
SLAU272C – May 2011 – Revised November 2013
CPUX
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