How to resolve the algorithm Show ASCII table step by step in the 6502 Assembly programming language

Published on 12 May 2024 09:40 PM
#6502 assembly

How to resolve the algorithm Show ASCII table step by step in the 6502 Assembly programming language

Table of Contents

Problem Statement

Show  the ASCII character set  from values   32   to   127   (decimal)   in a table format.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Show ASCII table step by step in the 6502 Assembly programming language

Source code in the 6502 programming language

==========================================================================
; task    : show ascii table 
; language: 6502 Assembly
; for:    : rosettacode.org
; run     : on a Commodore 64 with command
;           sys 49152
;
; same logic of "Commodore BASIC"
;
; assembler win2c64 by Aart Bik
; http://www.aartbik.com/
;
; 2020-05-01 alvalongo
;==========================================================================
; constants 
cr         = 13    ; carriage-return
white      = 5     ; color white
; ----------------------------------------------
; memory on zero page
linnum     = $14
; ----------------------------------------------
; kernel routines
linstr    = $bdcd   ; C64 ROM       : convert a 16-bit value to string and print on current device (default screen)
chrout    = $ffd2   ; C64 ROM kernel: output a character to current device, default screen
			        ;                 use $fded for Apple 2
;
; ----------------------------------------------
;
        .org   $c000   ; start at free RAM, on Commodore 64
; ----------------------------------------------
l100    lda #147       ; clear screen
        jsr chrout
        ;
l110    lda #14         ;character set 2, upper/lower case mode
        jsr chrout
        ;
        lda #white      ; color for characters
        jsr chrout
        ;
l120    lda #
        ldx #>msg1
        jsr prtmsg
        ;
l130    lda #
        ldx #>msg2
        jsr prtmsg
        ;
l140    lda #cr
        jsr chrout
        ;
l150    lda #0
        sta row
        ;
l160    lda #0
        sta column
        ;
l170    clc
        lda row
        adc #32
        sta ascii
        lda column
        asl     ; times 2,  2
        asl     ; times 2,  4
        asl     ; times 2,  8
        asl     ; times 2, 16
        adc ascii
        sta ascii
        ;
l180    cmp #100
        bcs l185     ; equal or greater than
        lda #" "     ; a space before values less than 100
        jsr chrout
        ;
l185    ldx ascii
        lda #0
        jsr linstr       ; convert to string and print on screen
        lda #":"
        jsr chrout
        lda ascii
        jsr chrout
        lda #" "
        jsr chrout
        ;
l190    inc column  ; next column
        lda column
        cmp #5
        bcc l170
        beq l170
        ;
l200    lda #cr
        jsr chrout
        ;
l210    inc row    ; next row
        lda row
        cmp #15
        bcc l160
        beq l160
        ;
l220    rts      ; return to operating system
; ----------------------------------------------
; print message
;
prtmsg  sta linnum
        stx linnum+1
        ldy #0
l310    lda (linnum),y
        beq l320
        jsr chrout
        iny
        bne l310
l320    lda #cr
        jsr chrout
        rts 
; ----------------------------------------------
msg1    .byte "COMMODORE 64 - BASIC V2",0
msg2    .byte "CHARACTER SET 2 UPPER/LOWER CASE MODE",0
row     .byte 0
column  .byte 0
ascii   .byte 0

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