Q. Show the Simple Arithmetic Application?

The question is why can't we simply employ XCHG instruction with 2 memory variables as operand? To answer the question let's look into a number of constraints for XCHG &MOV instructions:

MOV instruction has subsequent operands and constraints:

• IP and CS may never be destination operands in MOV
• Immediate memory variables and data value may not be moved to segment registers
• Source and destination operands must be of the same size
• Both operands can't be memory locations
• If source is immediate data it should not exceed 255 (FFh) for an 8-bit destination or 65,535 (FFFFh) for a 16-bit destination.

Statement MOV AL, VALUE1 copies the VALUE1 which is 0Ah in AL register:

Instruction XCHG   AL, VALUE2 exchanges the value of AL with VALUE2

Now AL and VALUE2 contains and values as under:

StatementMOV VALUE1, AL; now puts value of AL to VALUE1. 

So desired exchange is complete 

Simple Arithmetic Application