Exchange 2 Blocks of Data

    MOV 20h, #01h
    MOV 21h, #02h
    MOV 22h, #03h
    MOV 23h, #04h
    MOV 24h, #05h
    MOV 25h, #06h
    MOV 26h, #07h
    MOV 27h, #08h
    MOV 28h, #09h
    MOV 29h, #0Ah

    MOV 40h, #0Ah
    MOV 41h, #09h
    MOV 42h, #08h
    MOV 43h, #07h
    MOV 44h, #06h
    MOV 45h, #05h
    MOV 46h, #04h
    MOV 47h, #03h
    MOV 48h, #02h
    MOV 49h, #01h

    MOV R2, #0Ah    ;counter
    MOV R0, #20h    ;place A
    MOV R1, #40h    ;place B
loop:   MOV A, @R0
    MOV R3, A
    MOV A, @R1
    MOV @R0, A
    MOV A, R3
    MOV @R1, A
    INC R0
    INC R1
    DJNZ R2, loop
    END