SPO600- Math and strings Lab(Lab 3)

In this lab, I was asked to write a program that meets following criteria,

1. Program must work in the 6502 Emulator.

2. Output must be shown to both the character screen as well as the graphics or bitmapped screen.

3. Program must take user input from keyboard in some form.

4. Also I must use some arithmetic or math instructions

For my program, I have selected one of the program wrote by our course professor. I got this program from github. As I am still learning the language, so I have decided to modify that code to produce a bit different kind of output than the original one without giving away the main intend. 

So the original program would ask the user to select a color from a given list, which will then be shown in the bitmapped display. Here I have changed the input text that was asked to the user as I have modified the program in such a way that the selection prompt will start from the light green which is not at the top of the list instead of the original one which was black. Additionally, I modified the code to fill only 2 pages of the display instead of the whole screen. The modified code and output is showing below:

Modified code:

; Colour selector - live updates

; (C)2020 Chris Tyler - Seneca College

; Modified by Naziur Rahman khan

; Licensed under the GPLv2+ - see LICENSE file


; ROM routine entry points

define SCINIT $ff81 ; initialize/clear screen

define CHRIN $ffcf ; input character from keyboard

define CHROUT $ffd2 ; output character to screen

define SCREEN $ffed ; get screen size

define PLOT $fff0 ; get/set cursor coordinates


; zeropage variables

define PRINT_PTR $00

define PRINT_PTR_H $01

define CURRENT $02

define SCRN_PTR $03

define SCRN_PTR_H $04


; constants


; --------------------------------------------------------


jsr SCINIT


jsr PRINT

dcb "B","l","a","c","k",$0d

dcb "W","h","i","t","e",$0d

dcb "R","e","d",$0d

dcb "C","y","a","n",$0d

dcb "P","u","r","p","l","e",$0d

dcb "G","r","e","e","n",$0d

dcb "B","l","u","e",$0d

dcb "Y","e","l","l","o","w",$0d

dcb "O","r","a","n","g","e",$0d

dcb "B","r","o","w","n",$0d

dcb "L","i","g","h","t",32,"r","e","d",$0d

dcb "D","a","r","k",32,"g","r","e","y",$0d

dcb "G","r","e","y",$0d

dcb "L","i","g","h","t",32,"g","r","e","e","n",$0d

dcb "L","i","g","h","t",32,"b","l","u","e",$0d

dcb "L","i","g","h","t",32,"g","r","e","y",$0d

dcb $0d

dcb "C","h","o","o","s","e",32,"a",32,"c","o","l","o","r",32

dcb "f","r","o","m",32,"t","h","e",32,"a","b","o","v","e",32,"l","i","s","t",32,"t","o",32,"s","e","e",32,"i","t",32

dcb "o","n",32,"t","h","e",32,"f","i","r","s","t",32,"t","w","o",32,"p","a","g","e",32,"o","f",32,"t","h","e",32,"b","i","t","m","a","p","p","e","d",32

dcb "d","i","s","p","l","a","y",".",$0d

dcb 00



lda #$0d


get_colour: jsr SELECT


ldy #$00

sty SCRN_PTR

ldx #$02

stx SCRN_PTR_H

ldx #$02 ; number of pages to fill


draw: sta (SCRN_PTR),y

iny

bne draw


inc SCRN_PTR_H

dex

bne draw


jmp get_colour



; -----------------------------------------------------------

; SELECT :: select one line from the screen


SELECT: sta CURRENT


show_and_go: jsr HIGHLIGHT


getkey: jsr CHRIN

cmp #$80 ; cursor up

bne try_down


lda CURRENT

beq getkey

jsr HIGHLIGHT

dec CURRENT

jmp return


try_down: cmp #$82 ; cursor down

bne getkey


lda CURRENT

cmp #$0f

beq getkey

jsr HIGHLIGHT

inc CURRENT


return: lda CURRENT


rts



; --------------------------------------------------------

;

; Highlight :: highlight the CURRENT line on the display


HIGHLIGHT: ldy CURRENT

ldx #$00

clc

jsr PLOT



highlight_next: sec

jsr PLOT

eor #$80

jsr CHROUT


inx

cpx #20

bne highlight_next


rts



; --------------------------------------------------------

; Print a message

; 

; Prints the message in memory immediately after the 

; JSR PRINT. The message must be null-terminated and

; 255 characters maximum in length.


PRINT: pla

clc

adc #$01

sta PRINT_PTR

pla

sta PRINT_PTR_H


tya

pha


ldy #$00

print_next: lda (PRINT_PTR),y

beq print_done

jsr CHROUT

iny

jmp print_next


print_done: tya

clc

adc PRINT_PTR

sta PRINT_PTR


lda PRINT_PTR_H

adc #$00

sta PRINT_PTR_H


pla

tay


lda PRINT_PTR_H

pha

lda PRINT_PTR

pha


rts


                                                  The above part was the modified code

Output:



Compared to last few labs, I am feeling more comfortable with the emulator now as I can see the output of my very own customized code blocks. I am excited to continue experimenting in this emulator and build my own piece of program all by myself. 

Code courtesy: This code was taken from this link mentioned in the resources by the course instructor.

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