;------------------------------------------------------
;
; Description: Creates a SC1 based 64 columns mode by mixing two VRAM pages
;
; The new VRAM map is:
; 0000-07FF : Pattern table 1
; 0800-0FFF : Pattern table 2
; 1400-16FF : Name table 1
; 1800-1AFF : Name table 2
;
; Color, sprites & palette (MSX2) tables addresses are untouched
;
; Use asMSX to compile (although is easily adapted to other assemblers)
;
;------------------------------------------------------

        .bios
        .page 1
        .rom
.start MAIN
       
RG2SAV equ     $F3E1
RG4SAV equ     $F3E3

MAIN: ; Initializes SC1 with 15,1,1 colors & 32 columns
ld a,32
ld [$F3AF],a
ld a,15
ld [$F3E9],a
ld a,1
ld [$F3EA],a
ld [$F3EB],a
call INIT32

; fills both name tables with spaces (prolly useless)
ld hl,$1400
ld bc,$0700
ld a,32
call FILVRM

; dump to VRAM a 4 pixels right shifted font, based on the old one
ld hl,$0800+32*8
call SETWRT
ld hl,FONT4x8
ld bc,768
@@LOOP: ld a,[hl]
                and $F0
                rrca
                rrca
                rrca
                rrca           
out ($98),a
inc hl
dec bc
ld a,b
or c
jr nz,@@LOOP

; dump the font to VRAM
ld hl,FONT4x8
ld de,$0000+32*8
ld bc,768
call LDIRVM

                ; Sets active name table to address $1400
ld bc,$0502
call WRTVDP

; installs interupt hook
        call INSTALLISR

; prints an example text
ld hl,TXT1
ld de,$0000 ; X(0-63)Y(0-23)
call PUTS
@@HANG: jp @@HANG


;------------------------------------------------------
;
; Description: Prints a string
; Input: D = coord. X (0-63), E = coord. Y (0-23)
; Output: nothing
; Modifies: AF,HL,DE,BC
;
;------------------------------------------------------
PUTS: push hl
                ld h,0         
                ld l,e          ; Y
                add hl,hl       
                add hl,hl       
                add hl,hl       
                add hl,hl       
                add hl,hl       ; Y*32
ld b,$14
ld a,d
sra a
ld c,a ; X\2
add hl,bc       ; HL=NAME table position
call SETWRT
ex de,hl ; DE=VRAM
pop hl ; HL=TXT1
ld b,2         ; prints even & odd positions
@@LOOP2: push hl
@@LOOP1:        ld a,[hl]
or a
jr z,@@FINTXT
out ($98),a     ; outputs even char
inc hl
ld a,[hl]
or a
jr z,@@FINTXT
inc hl
jr @@LOOP1
@@FINTXT:       ld hl,$400      ; switch to odd chars
add hl,de
call SETWRT
pop hl
inc hl
djnz @@LOOP2
ret

;
; Interrupt routine
;
ISR: di
exx
        in a,($99)
        ld b,5
ld a,[VALUE]
inc a
ld [VALUE],a
; sets flag to 0-1 values
and 1
jr z,@@NOPAGE2
inc b
@@NOPAGE2: out ($99),a
ld [RG4SAV],a
ld a,$84
; sets active pattern table
out ($99),a
ld a,b
out ($99),a
ld [RG2SAV],a
ld a,$82
; sets active name table
out ($99),a
        exx
        ei
        ret

;
; Installs interrupt hook
;
INSTALLISR: di
        ld hl,$FD9F
        ld de,HOOK
        ld bc,5
        ldir
        ld a,$C3
        ld hl,ISR
        ld [$FD9F],a
        ld [$FD9F+1],hl
        ei
        ret

;
; Uninstalls interrupt hook (not used in this example! :P)
;
REMOVEISR: di
        ld hl,HOOK
        ld de,$FD9F
        ld bc,5
        ldir
        ei
        ret

;
; Example text
;
TXT1: DB "En un agujero en el suelo, vivia un hobbit."
DB " No un agujero humedo, sucio, repugnante, "
DB "con restos de gusanos y olor a fango, ni "
DB "tampoco un agujero seco, desnudo y arenoso, "
DB "sin nada en que sentarse o que comer: era un "
DB "agujero-hobbit, y eso significa comodidad. Tenia"
DB " una puerta redonda, perfecta como un ojo de "
DB "buey, pintada de verde, con una manilla de bronce"
DB " dorada y brillante, justo en el medio. La puerta"
DB " se abria a un vestibulo cilindrico, como un tunel:"
DB " un tunel muy comodo, sin humos, con paredes "
DB "revestidas de madera y suelos enlosados y "
DB "alfombrados, provisto de sillas barnizadas, y "
DB "montones y montones de perchas para sombreros "
DB "y abrigos; el hobbit era aficionado a las visitas.",0

;
; Guess what?. It's a 4x8 font...
;
FONT4x8:
DB $00,$00,$00,$00,$00,$00,$00,$00
DB $40,$40,$40,$40,$40,$00,$40,$00
DB $A0,$A0,$00,$00,$00,$00,$00,$00
DB $A0,$A0,$F0,$A0,$F0,$A0,$A0,$00
DB $40,$E0,$80,$40,$20,$E0,$40,$00
DB $A0,$20,$40,$40,$40,$80,$A0,$00
DB $40,$A0,$40,$80,$C0,$A0,$50,$00
DB $40,$40,$00,$00,$00,$00,$00,$00
DB $40,$80,$80,$80,$80,$80,$40,$00
DB $40,$20,$20,$20,$20,$20,$40,$00
DB $00,$00,$A0,$40,$A0,$00,$00,$00
DB $00,$00,$40,$E0,$40,$00,$00,$00
DB $00,$00,$00,$00,$00,$20,$40,$00
DB $00,$00,$00,$E0,$00,$00,$00,$00
DB $00,$00,$00,$00,$00,$00,$40,$00
DB $20,$20,$40,$40,$40,$80,$80,$00
DB $40,$A0,$A0,$A0,$A0,$A0,$40,$00
DB $40,$C0,$40,$40,$40,$40,$E0,$00
DB $40,$A0,$20,$40,$80,$80,$E0,$00
DB $40,$A0,$20,$40,$20,$A0,$40,$00
DB $A0,$A0,$A0,$E0,$20,$20,$20,$00
DB $E0,$80,$80,$C0,$20,$A0,$40,$00
DB $40,$A0,$80,$C0,$A0,$A0,$40,$00
DB $E0,$20,$20,$40,$40,$40,$40,$00
DB $40,$A0,$A0,$40,$A0,$A0,$40,$00
DB $40,$A0,$A0,$60,$20,$A0,$40,$00
DB $00,$00,$00,$40,$00,$00,$40,$00
DB $00,$00,$00,$20,$00,$20,$40,$00
DB $00,$20,$40,$80,$40,$20,$00,$00
DB $00,$00,$E0,$00,$E0,$00,$00,$00
DB $00,$80,$40,$20,$40,$80,$00,$00
DB $40,$A0,$A0,$20,$40,$00,$40,$00
DB $40,$A0,$A0,$C0,$80,$A0,$40,$00
DB $40,$A0,$A0,$E0,$A0,$A0,$A0,$00
DB $C0,$A0,$A0,$C0,$A0,$A0,$C0,$00
DB $40,$A0,$80,$80,$80,$A0,$40,$00
DB $C0,$A0,$A0,$A0,$A0,$A0,$C0,$00
DB $E0,$80,$80,$C0,$80,$80,$E0,$00
DB $E0,$80,$80,$C0,$80,$80,$80,$00
DB $40,$A0,$80,$A0,$A0,$A0,$40,$00
DB $A0,$A0,$A0,$E0,$A0,$A0,$A0,$00
DB $40,$40,$40,$40,$40,$40,$40,$00
DB $20,$20,$20,$20,$20,$A0,$40,$00
DB $A0,$A0,$A0,$C0,$A0,$A0,$A0,$00
DB $80,$80,$80,$80,$80,$80,$E0,$00
DB $A0,$E0,$E0,$A0,$A0,$A0,$A0,$00
DB $E0,$A0,$A0,$A0,$A0,$A0,$A0,$00
DB $40,$A0,$A0,$A0,$A0,$A0,$40,$00
DB $C0,$A0,$A0,$C0,$80,$80,$80,$00
DB $40,$A0,$A0,$A0,$A0,$C0,$20,$00
DB $C0,$A0,$A0,$C0,$A0,$A0,$A0,$00
DB $40,$A0,$80,$40,$20,$A0,$40,$00
DB $E0,$40,$40,$40,$40,$40,$40,$00
DB $A0,$A0,$A0,$A0,$A0,$A0,$60,$00
DB $A0,$A0,$A0,$A0,$A0,$A0,$40,$00
DB $A0,$A0,$A0,$A0,$E0,$E0,$A0,$00
DB $A0,$A0,$A0,$40,$A0,$A0,$A0,$00
DB $A0,$A0,$A0,$40,$40,$40,$40,$00
DB $E0,$20,$20,$40,$80,$80,$E0,$00
DB $60,$40,$40,$40,$40,$40,$60,$00
DB $80,$80,$40,$40,$40,$20,$20,$00
DB $60,$20,$20,$20,$20,$20,$60,$00
DB $40,$A0,$00,$00,$00,$00,$00,$00
DB $00,$00,$00,$00,$00,$00,$E0,$00
DB $40,$20,$00,$00,$00,$00,$00,$00
DB $00,$00,$00,$40,$A0,$A0,$60,$00
DB $00,$80,$80,$C0,$A0,$A0,$40,$00
DB $00,$00,$00,$60,$80,$80,$60,$00
DB $00,$20,$20,$60,$A0,$A0,$40,$00
DB $00,$00,$00,$60,$A0,$C0,$60,$00
DB $00,$20,$40,$E0,$40,$40,$40,$00
DB $00,$00,$00,$40,$A0,$60,$C0,$00
DB $00,$80,$80,$C0,$A0,$A0,$A0,$00
DB $00,$00,$40,$00,$40,$40,$40,$00
DB $00,$00,$40,$00,$40,$40,$80,$00
DB $00,$80,$A0,$C0,$A0,$A0,$A0,$00
DB $00,$40,$40,$40,$40,$40,$40,$00
DB $00,$00,$00,$A0,$E0,$A0,$A0,$00
DB $00,$00,$00,$E0,$A0,$A0,$A0,$00
DB $00,$00,$00,$40,$A0,$A0,$40,$00
DB $00,$00,$00,$C0,$A0,$C0,$80,$00
DB $00,$00,$00,$40,$A0,$60,$20,$00
DB $00,$00,$00,$A0,$C0,$80,$80,$00
DB $00,$00,$00,$20,$40,$20,$C0,$00
DB $00,$40,$40,$E0,$40,$40,$40,$00
DB $00,$00,$00,$A0,$A0,$A0,$60,$00
DB $00,$00,$00,$A0,$A0,$A0,$40,$00
DB $00,$00,$00,$A0,$A0,$E0,$A0,$00
DB $00,$00,$00,$A0,$40,$40,$A0,$00
DB $00,$00,$00,$A0,$A0,$40,$C0,$00
DB $00,$00,$00,$E0,$60,$80,$E0,$00
DB $20,$40,$40,$80,$40,$40,$20,$00
DB $40,$40,$40,$40,$40,$40,$40,$00
DB $80,$40,$40,$20,$40,$40,$80,$00
DB $40,$F0,$20,$00,$00,$00,$00,$00

;
; RAM variables
;
.page 3

VALUE: DS 1
HOOK: DS 5