bar 6502

//making simple rasterbars
//by Knoeki of Digital Sounds System
//
//was coded and proven to work in Turbo Assembler 5.2 (Cyberpunx RR)
//
//should be compatible with most assemblers out there..
//
//                                                          enjoy //)

.pc = $0801 "Basic Program"

:BasicUpstart($0810)

.pc =$0810 "Program"


         sei              //disable interrupts

         lda #$00         //load $00 into A
         sta $d011        //turn off screen. (now you have only borders!)
         sta $d020        //make border black.

main:    ldy #56   //load $7a into Y. this is the line where our rasterbar will start. od linii 56 z góry
         ldx #$00         //load $00 into X
loop:    lda colors,x     //load value at label 'colors' plus x into a. if we don't add x, only the first
                          //value from our color-table will be read.

         cpy $d012        //ComPare current value in Y with the current rasterposition.
         bne *-3          //is the value of Y not equal to current rasterposition? then jump back 3 bytes (to cpy).

         sta $d020        //if it IS equal, store the current value of A (a color of our rasterbar)
                          //into the bordercolour

         cpx #1          //compare X to #51 (decimal). have we had all lines of our bar yet?
         beq main         //Branch if EQual. if yes, jump to main.

         inx              //increase X. so now we're gonna read the next color out of the table.
         iny              //increase Y. go to the next rasterline.

         jmp loop         //jump to loop.


colors:
         .byte %00000001,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111
         .byte %00001111,%00001111,%00001111,%00001111,%00001111,%00001111

         .byte $ff




//-----------------------------------------------------------------
//
//if everything goes correctly, you should have a blue rasterbar on
//the middle of your screen. play with the values a bit, and see
//what you can do with it... =)