;
; hires_payfield.asm
;
; This example sets up a high resolution, interlaced display with one
; bitplane.  This example also relies on the include file hw_examples.i.

;
        LEA     CUSTOM,a0               ; Address of custom chips
        MOVE.W  #$9204,BPLCON0(a0)      ; Hires, one bitplane, interlaced
        MOVE.W  #0,BPLCON1(a0)          ; Horizontal scroll value = 0
        MOVE.W  #80,BPL1MOD(a0)         ; Modulo = 80 for odd bitplanes
        MOVE.W  #80,BPL2MOD(a0)         ; Ditto for even bitplanes
        MOVE.W  #$003C,DDFSTRT(a0)      ; Set data-fetch start for Hires
        MOVE.W  #$00D4,DDFSTOP(a0)      ; Set data-fetch stop
        MOVE.W  #$2C81,DIWSTRT(a0)      ; Set display window start
        MOVE.W  #$F4C1,DIWSTOP(a0)      ; Set display window stop
;
;  Set up color registers
;
        MOVE.W  #$000F,COLOR00(a0)      ; Background color = blue
        MOVE.W  #$0FFF,COLOR01(a0)      ; Foreground color = white
;
;  Set up bitplane at $20000
;
        LEA     $20000,a1       ; Point a1 at bitplane
        LEA     CHARLIST(pc),a2 ; a2 points at character data
        MOVE.W  #400,d1         ; Write 400 lines of data
        MOVE.W  #20,d0          ; Write 20 long words per line
L1:
        MOVE.L  (a2),(a1)+      ; Write a long word
        DBRA    d0,L1           ; Decrement counter and loop until full...
;
        MOVE.W  #20,d0          ; Reset long word counter
        ADDQ.L  #4,a2           ; Point at next word in char list
        CMPI.L  #$FFFFFFFF,(a2) ; End of char list?
        BNE     L2
        LEA     CHARLIST(pc),a2 ; Yes, reset a2 to beginning of list
L2:     DBRA    d1,L1           ; Decrement line counter and loop until done...
;
;  Start DMA
;
        MOVE.W  #(DMAF_SETCLR!DMAF_RASTER!DMAF_MASTER),DMACON(a0)
                                ; Enable bitplane DMA only, no Copper

; Because this example has no Copper list, it sits in a loop waiting
; for the vertical blanking interval.  When it comes, you check the LOF
; ( long frame ) bit in VPOSR.  If LOF = 0, this is a short frame and the
; bitplane pointers are set to point to $20050.  If LOF = 1, then this is
; a long frame and the bitplane pointers are set to point to $20000.  This
; keeps the long and short frames in the right relationship to each other.

VLOOP:  MOVE.W  INTREQR(a0),d0          ; Read interrupt requests
        AND.W   #$0020,d0               ; Mask off all but vertical blank
        BEQ     VLOOP                   ; Loop until vertical blank comes
        MOVE.W  #$0020,INTREQ(a0)       ; Reset vertical interrupt
        MOVE.W  VPOSR(a0),d0            ; Read LOF bit into d0 bit 15
        BPL     VL1                     ; If LOF = 0, jump
        MOVE.L  #$20000,BPL1PTH(a0)     ; LOF = 1, point to $20000
        BRA     VLOOP                   ; Back to top
VL1:
        MOVE.L  #$20050,BPL1PTH(a0)     ; LOF = 0, point to $20050
        BRA     VLOOP                   ; Back to top
;
;  Character list
;
CHARLIST:
        DC.L    $18FC3DF0,$3C6666D8,$3C66C0CC,$667CC0CC
        DC.L    $7E66C0CC,$C36666D8,$C3FC3DF0,$00000000
        DC.L    $FFFFFFFF

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