Transfer the contents of the storage unit with the address of 40H (that is, 48H) to the accumulator a ... that is, A=48H.

MOV R 1，A

Transfer the value of accumulator a to register R 1 for 48 hours. That is, R 1=48H.

MOV 40H，@R 1

This statement puts the value of the storage unit pointed by the register into the 40H unit for storage.

The result is (40H)=90H.

MOV @R 1，A

This statement transfers the value of accumulator A to the memory location pointed by register R 1

The result is (48H)=48H.

XCH A，R 1

This statement is used to exchange the values of register R 1 and accumulator a.

At this time, the values of a and R 1 are both 48H.