6502 multiplier

8bitmul.asm

processor 6502

prod            EQU $0380
multiplier      EQU $0381
multiplicand    EQU $0382

    INCLUDE basic.rom
    INCLUDE common.asm
    
    +autoRun

    ;  mul.er   prod
    ;  00101000 00000000
    ;  01010000 00000000
    ;  10100000 00000000
    ;C 01000000 00110000
    ;  10000000 01100000
    ;C 00000000 11110000
    ;  00000001 11100000
    ;  00000011 11000000
    ;  00000111 10000000

    ldx #48 ; 00110000
    lda #40 ; 00101000
    ;a * x -> prod (low), multiplier(high)

    stx multiplicand
    sta multiplier
    lda #$0
    sta prod
    ldx #$08
n:
    asl prod
    rol multiplier ; add the carry from prod to multiplier
    bcc noadd
    lda prod
    clc
    adc multiplicand
    sta prod

noadd:
    dex
    bne n

    ldx prod
    lda multiplier
    jsr linprt
    rts

    ECHO *