Introduction
Hello my friend, welcome back to the second part of the string lab. In this lab, we decided to create 2 programs and split it into part 1 and part 2 using 6502 assembly language. In the first part, we created an adding calculator and now what you are reading is the second part of this lab. In this part, we decided to create a color selector. This program allows the user to choose the color on the right side screen by using keystroke, then the program will print the certain color on the screen.
Steps
- Create a ROM to print the color string on the screen.
- Create the up key and down key then assign the functionality. It will allow users to select the color string on the screen.
- Print the title of the color string.
- Print 15 color strings using loop
- Use a loop to highlight the name string that the user has selected.
- Use draw_screen loop to change the color of the pixels.
Code
define SCINIT $ff81 ; initialize/clear screen
define CHROUT $ffd2 ; output character to screen
define COLOUR $10
define COLOUR_INDEX $11
define POINTER $40
define POINTER_H $41
define UP_KEY $80
define DOWN_KEY $82
lda #$00
sta COLOUR
sta COLOUR_INDEX
jsr initializePrint
getKey:
lda $ff
sty $ff
cmp #UP_KEY
beq decrementKey
cmp #DOWN_KEY
beq incrementKey
jmp getKey
decrementKey:
lda COLOUR
cmp #$01
bpl decrementColour
jmp getKey
decrementColour:
dec COLOUR
jsr initializePrint
jsr initializePaint
jmp getKey
incrementKey:
lda COLOUR
cmp #$0f
bmi incrementColour
jmp getKey
incrementColour:
inc COLOUR
jsr initializePrint
jsr initializePaint
jmp getKey
initializePrint:
jsr SCINIT
ldy #$00
writeTitle:
lda title,y
beq titleDone
jsr CHROUT
iny
bne writeTitle
titleDone:
lda #$00
sta COLOUR_INDEX
startColour:
ora #$00
ldy #$00
colourName:
jsr selectedColour
beq afterWriting
jsr highlightLine
jsr CHROUT
iny
bne colourName
afterWriting:
inc COLOUR_INDEX
lda COLOUR_INDEX
cmp #$10
bne startColour
selectedColour:
lda COLOUR_INDEX
cmp #$00
beq printColour0
cmp #$01
beq printColour1
cmp #$02
beq printColour2
cmp #$03
beq printColour3
cmp #$04
beq printColour4
cmp #$05
beq printColour5
cmp #$06
beq printColour6
cmp #$07
beq printColour7
cmp #$08
beq printColour8
cmp #$09
beq printColour9
cmp #$0a
beq printColour10
cmp #$0b
beq printColour11
cmp #$0c
beq printColour12
cmp #$0d
beq printColour13
cmp #$0e
beq printColour14
cmp #$0f
beq printColour15
rts
printColour0:
lda colour0,y
rts
printColour1:
lda colour1,y
rts
printColour2:
lda colour2,y
rts
printColour3:
lda colour3,y
rts
printColour4:
lda colour4,y
rts
printColour5:
lda colour5,y
rts
printColour6:
lda colour6,y
rts
printColour7:
lda colour7,y
rts
printColour8:
lda colour8,y
rts
printColour9:
lda colour9,y
rts
printColour10:
lda colour10,y
rts
printColour11:
lda colour11,y
rts
printColour12:
lda colour12,y
rts
printColour13:
lda colour13,y
rts
printColour14:
lda colour14,y
rts
printColour15:
lda colour15,y
rts
highlightLine:
ldx COLOUR_INDEX
cpx COLOUR
beq highlight
ora #$00
rts
highlight:
ora #$80
rts
initializePaint:
lda #$00 ; set a pointer at $40 to point to $0200
sta POINTER
lda #$02
sta POINTER_H
ldy #$00
lda COLOUR
draw_screen:
sta ($40), y ; set pixel
iny ; increment index
bne draw_screen ; continue until done the page
inc $41 ; increment the page
ldx $41 ; get the page
cpx #$06 ; compare with 6
bne draw_screen ; continue until done all pages
rts
title:
dcb "L","i","s","t",32,"o","f",32,"C","o","l","o","u","r","s",":",13
dcb 00
colour0:
dcb "B","l","a","c","k",13
dcb 00
colour1:
dcb "W","h","i","t","e",13
dcb 00
colour2:
dcb "R","e","d",13
dcb 00
colour3:
dcb "C","y","a","n",13
dcb 00
colour4:
dcb "P","u","r","p","l","e",13
dcb 00
colour5:
dcb "G","r","e","e","n",13
dcb 00
colour6:
dcb "B","l","u","e",13
dcb 00
colour7:
dcb "Y","e","l","l","o","w",13
dcb 00
colour8:
dcb "O","r","a","n","g","e",13
dcb 00
colour9:
dcb "B","r","o","w","n",13
dcb 00
colour10:
dcb "L","i","g","h","t",32,"r","e","d",13
dcb 00
colour11:
dcb "D","a","r","k",32,"g","r","e","y",13
dcb 00
colour12:
dcb "G","r","e","y",13
dcb 00
colour13:
dcb "L","i","g","h","t",32,"g","r","e","e","n",13
dcb 00
colour14:
dcb "L","i","g","h","t",32,"b","l","u","e",13
dcb 00
colour15:
dcb "L","i","g","h","t",32,"g","r","e","y",13
dcb 00
The sample results :
Reflection
In lab 4 part 2, we created a color selector using assembly language. It is a new challenge for us. The most tedious thing is to use different loops to print the color strings and highlight the user selections. Afterwards, we also have to use a loop to change the color pixels. The assembly language is hard for me as a beginner to learn and work with it in 4 different labs. I can not say I'm a master of it because I’m not hundred-percent familiar with the syntax and the coding logic like other higher programming languages. But I’m glad to learn and work on it for almost the whole semester and it shows me a view of a low level programming language that I never touched before, it also helps me to understand the higher-level programming language deeply on the storage and ram view.
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