;programme multiplying 2-byte numbers without signs
; numbers are stored in internal data memory
; result is stored in registers R7..R4 (R4-LSB)
N1  equ 28h
N2  equ     30h

    mov N1,#low(2000)
    mov N1+1,#high(2000)

    mov N2,#low(3000)
    mov N2+1,#high(3000)

    mov a,N1    ;A <-LSB(numb1)
    mov     b,N2    ;B <-LSB(numb2)
    mul     ab  ;BA := product
    ;storing results
    mov r4,a
    mov     r5,b

    mov a,N1+1  ;A <-MSB(numb2)
    mov b,N2+1  ;B <-MSB(numb2)
    mul     ab  ;BA := product
    ;storing results
    mov r6,a
    mov     r7,b

    mov a,N1    ;A <-lSB(numb2)
    mov b,N2+1  ;B <-MSB(numb2)
    mul     ab  ;BA := product
    ;adding results to r7..r5
    add a,r5
    mov     r5,a
    mov a,b
    addc    a,r6
    mov r6,a
    clr a
    addc    a,r7    ;updating R7 with possible overflow
    mov r7,a

    mov a,N1+1  ;A <-MSB(numb2)
    mov b,N2    ;B <-LSB(numb2)
    mul     ab  ;BA := product
    ;adding results to r7..r5
    add a,r5
    mov     r5,a
    mov a,b
    addc    a,r6
    mov r6,a
    clr a
    addc    a,r7    ;updating R7 with possible overflow
    mov r7,a

    sjmp $

    end