C02/vcs/colors4.c02

/* Atari VCS Color Bars Program */

#pragma origin $F800    //2k Cartridge
#include <vcshead.h02>  //TIA and RIOT Registers
#include <vcsinit.h02>  //Initialize VCS

zeropage char clrbkg; //Color Background
zeropage char clrofs; //Color Offset
zeropage char clrmsk; //Color/B&W Mask

zeropage char score;  //Two Digit BCD Score
zeropage char timer;  //Two Digit BDC Timer
zeropage char scrone; //Offset into Ones Digit
zeropage char tmrone;
zeropage char scrten; //Offset into Tens Digit
zeropage char tmrten;
zeropage char scrgfx; //Score Graphics Data
zeropage char tmrgfx; //Score Timer Graphics
 
zeropage char temp; //Scratch Variable

/* Generate Ones Digit Offset */
char ofsone() {
  temp = A & $0F;
  temp++;
  A<<; A<<;
  return A + temp;
}

/* Generate Tens Digit Offset */
char ofsten() {
  A = A & $F0;
  A>>; A>>;
  temp = A;
  temp++;
  A>>; A>>;
  return A + temp;
}

/* Prepare Score and Timer for Display */
void prepst() {
  scrone = ofsone(score);
  scrten = ofsten(score);
  tmrone = ofsone(timer);
  tmrten = ofsten(timer);
}

/* Display Score and Timer */
void dispst() {
  X = 5; //5 lines in digit
  
}

ScoreLoop:              ;   43 - cycle after bpl ScoreLoop
        ldy DigitTens   ; 3 46 - get the tens digit offset for the Score
        lda DigitGfx,y  ; 5 51 -   use it to load the digit graphics
        and #$F0        ; 2 53 -   remove the graphics for the ones digit
        sta ScoreGfx    ; 3 56 -   and save it
        ldy DigitOnes   ; 3 59 - get the ones digit offset for the Score
        lda DigitGfx,y  ; 5 64 -   use it to load the digit graphics
        and #$0F        ; 2 66 -   remove the graphics for the tens digit
        ora ScoreGfx    ; 3 69 -   merge with the tens digit graphics
        sta ScoreGfx    ; 3 72 -   and save it
        sta WSYNC       ; 3 75 - wait for end of scanline
;---------------------------------------        
        sta PF1         ; 3  3 - @66-28, update playfield for Score dislay
        ldy DigitTens+1 ; 3  6 - get the left digit offset for the Timer
        lda DigitGfx,y  ; 5 11 -   use it to load the digit graphics
        and #$F0        ; 2 13 -   remove the graphics for the ones digit
        sta TimerGfx    ; 3 16 -   and save it
        ldy DigitOnes+1 ; 3 19 - get the ones digit offset for the Timer
        lda DigitGfx,y  ; 5 24 -   use it to load the digit graphics
        and #$0F        ; 2 26 -   remove the graphics for the tens digit
        ora TimerGfx    ; 3 29 -   merge with the tens digit graphics
        sta TimerGfx    ; 3 32 -   and save it
        jsr Sleep12     ;12 44 - waste some cycles
        sta PF1         ; 3 47 - @39-54, update playfield for Timer display
        ldy ScoreGfx    ; 3 50 - preload for next scanline 
        sta WSYNC       ; 3 53 - wait for end of scanline
;---------------------------------------
        sty PF1         ; 3  3 - @66-28, update playfield for the Score display
        inc DigitTens   ; 5  8 - advance for the next line of graphic data
        inc DigitTens+1 ; 5 13 - advance for the next line of graphic data
        inc DigitOnes   ; 5 18 - advance for the next line of graphic data
        inc DigitOnes+1 ; 5 23 - advance for the next line of graphic data
        jsr Sleep12     ;12 35 - waste some cycles
        dex             ; 2 37 - decrease the loop counter
        sta PF1         ; 3 40 - @39-54, update playfield for the Timer display
        bne ScoreLoop   ; 2 42 - (3 43) if dex != 0 then branch to ScoreLoop
        sta WSYNC       ; 3 45 - wait for end of scanline
;---------------------------------------
        stx PF1         ; 3  3 - x = 0, so this blanks out playfield        
        sta WSYNC       ; 3  6 - wait for end of scanline

/* Generate Vertical Sync Signal */
void vtsync() {
  X=49;     //49*64 Cycles (37 Scanlines)
  A=2;      //Set Bit 2 (D1)
  WSYNC=A;  //Wait for end of Scanline
  VSYNC=A;  //Turn On Vertical Sync
  TIM64T=X; //Set Timer
  WSYNC=A;  //Wait 2 More Scanlines
  WSYNC=A;
  A=0;      //Clear Bit 2 (D1)
  WSYNC=A;  //Wait for End of 3rd Scanline
  VSYNC=A;  //Turn Off Vertical Sync
  return;
}

/* Execute Vertical Blank Code */
void vtblnk() {
  clrmsk = (SWCHB & 8) ? $FF : $0F;
  if (SWCHB & 64) clrofs--; else clrofs++;
  A=0; //Clear All Bits
  return;
}

/* Execute Kernel Code */
void kernel() {
  do WSYNC=A; while(INTIM);
  VBLANK=0; //Turn Off Vertical Blank
  X=192; //Draw 192 Scanlines
  do {
    clrbkg = X;
    if (!SWCHB & 128) clrbkg<<;
    A = clrbkg + clrofs & clrmsk; //Set Background Color
    WSYNC = A;  //Wait for end of Scanline
    COLUBK = A; //Set Background Color
    X--;
  } while (X);
  return;
}

/* Execute Overscan Code */
void ovrscn() {
  WSYNC=A;     //Wait for end of Scanline
  A=2;         //Set Bit 2 (D1)
  VBLANK=A;    //Turn On Vertical Blank
  TIM64T = 32; //Delay 32*64 Cycles (27 Scanlines)
  do {
    WSYNC=A;  //Wait for end of Scanline
  } while(INTIM);
  return;
}

irqbrk: //Code to Execute when BRK Instruction is Encountered
main:  //Start of Program Code
  vtsync(); //Generate Vertical Sync Signal  
  vtblnk(); //Generate Vertical Blank Signal  
  kernel(); //Execute Kernal Code
  ovrscn(); //Execute Overscan Code
  goto main;

#include <vcsfoot.h02>  //Finalization Code