8086 CMP Instruction 
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Murugan Andezuthu Dharmaratnam | 
13 February 2021 | 
17711
13 February 2021 | 17711
CMP is a logical instruction which compares the desticaion and the source. It compares a byte or word in the specified source with a byte or word in the destination. The destination can be a register or a memory location but the source and the destination cannot both be memory locations. This instruction will not affect the source and destination, only the flags are set to indicate the results of the comparison. AF, OF, SF, ZF, PF, and CF are updated by the CMP instruction.
Types of operands supported
Instruction Operands
----------------------------
CMP REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate
result is not stored anywhere, flags are set (OF, SF, ZF, AF, PF, CF) according to the result.
Sample Code
CMP CX,BX
If you compare CX with BX. Depending on the value of CX and BX the below flags will be set
CF ZF SF CX = BX 0 1 0 Result of subtraction is 0 CX > BX 0 0 0 No borrow required, so CF = 0 CX < BX 1 0 1 Subtraction requires borrow, so CF = 1