Filter
Top Products
Instruction Set
3-34
RISC 16−Bit CPU
CMP[.W] Compare source and destination
CMP.B Compare source and destination
Syntax CMP src,dst or CMP.W src,dst
CMP.B src,dst
Operation dst + .NOT.src + 1
or
(dst − src)
Description The source operand is subtracted from the destination operand. This is
accomplished by adding the 1s complement of the source operand plus 1. The
two operands are not affected and the result is not stored; only the status bits
are affected.
Status Bits N: Set if result is negative, reset if positive (src >= dst)
Z: Set if result is zero, reset otherwise (src = dst)
C: Set if there is a carry from the MSB of the result, reset otherwise
V: Set if an arithmetic overflow occurs, otherwise reset
Mode Bits OSCOFF, CPUOFF, and GIE are not affected.
Example R5 and R6 are compared. If they are equal, the program continues at the label
EQUAL.
CMP R5,R6 ; R5 = R6?
JEQ EQUAL ; YES, JUMP
Example Two RAM blocks are compared. If they are not equal, the program branches
to the label ERROR.
MOV #NUM,R5 ; number of words to be compared
MOV #BLOCK1,R6 ; BLOCK1 start address in R6
MOV #BLOCK2,R7 ; BLOCK2 start address in R7
L$1 CMP @R6+,0(R7) ; Are Words equal? R6 increments
JNZ ERROR ; No, branch to ERROR
INCD R7 ; Increment R7 pointer
DEC R5 ; Are all words compared?
JNZ L$1 ; No, another compare
Example The RAM bytes addressed by EDE and TONI are compared. If they are equal,
the program continues at the label EQUAL.
CMP.B EDE,TONI ; MEM(EDE) = MEM(TONI)?
JEQ EQUAL ; YES, JUMP