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192lin.asm
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192lin.asm
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include macros.inc
; From tiles.as
extrn tiles
extrn colors
; From screen.as
extrn screen
NUM_TILES equ 20 ; 16 hex digits + 4 graphics
; VRAM tables for the V9938/V9958 GRAPHIC 3 mode
TAB_NAME equ 01800h ; Pattern name table
TAB_COLOR equ 02000h ; Color table
TAB_GENERATOR equ 00000h ; Pattern generator table
; ###################
; ## PROGRAM START ##
; ###################
start: di
; Save a pointer to the original interrupt handler
ld hl,(00038h+1)
ld (oldint),hl
; Install the new interrupt handler
ld hl,vblank
ld (00038h+1),hl
SET192LINES
SPRITESOFF
DISABLEHBLANK
ENABLEVBLANK
; Set the border color to something easy to see
ld a,7 ; Cyan
ld (RG0SAV+7),a
VDP 7
; Change to GRAPHIC 3 mode
call setgraphic3
; Set the start addresses of VRAM tables
ld a,000000110b ; Pattern name table in 01800h
VDP 2
ld a,010011111b ; Color table in 02000h
; 010000000b = Start at 02000h
; 000011111b = Use one tileset
VDP 3
xor a
VDP 10
xor a ; Pattern generator table in 00000h
VDP 4
; Copy the patterns (tiles) to VRAM
RAM2VRAM8 tiles,TAB_GENERATOR,NUM_TILES*8
RAM2VRAM8 colors,TAB_COLOR,NUM_TILES*8
; Copy the screen buffer to VRAM
RAM2VRAM16 screen,TAB_NAME,1024
ei
loop: jr loop
; ###############
; ## FUNCTIONS ##
; ###############
; Change to GRAPHIC 3 mode (SCREEN 4 in MSX-BASIC)
; Modifies: A
; Note: Interrupts must be disabled
setgraphic3: ld a,(RG0SAV+0)
and 011110001b
or 000000100b
ld (RG0SAV+0),a ; R#0 = ????010?b
VDP 0
ld a,(RG0SAV+1)
and 011100111b
ld (RG0SAV+1),a ; R#1 = ???00???b
VDP 1
ret
; Set VRAM address for read/write (only low 64KB)
; Input: DE = VRAM address (bits A0-A15)
; Modifies: A
; Note: Interrupts must be disabled
setvramaddr_w: ld a,d
rlca
rlca
and 000000011b
VDP 14 ; Send bits A16-A14 to VDP R#14
ld a,e
out (vdpport1),a ; Send bits A7-A0 to VDP (low 16KB)
ld a,d
and 000111111b
or 001000000b
out (vdpport1),a ; Send bits A13-A8 to VDP, for writing
ret
; ##########################
; ## INTERRUPT HANDLER(S) ##
; ##########################
vblank: ; Check whether the VDP generated the interrupt
RDVDP 0
and 010000000b
jr nz,vblank.2
; Not a VDP interrupt, ignore it
ei
ret
vblank.2:
; Increase the VDP's vertical scroll register
ld a,(RG8SAV+23)
inc a
ld (RG8SAV+23),a
VDP 23
; Re-enable interrupts and return to the main loop
ei
ret
; ###############
; ## VARIABLES ##
; ###############
oldint: defw 0 ; Pointer to the original interrupt handler