[Coco] Setting graphics modes with Assembly

[Fedor Steeman]

Hi all,

I have been studying Chris Lomont's reference guide and, combined with your
help, I am starting to come to grips with it. One thing I don't get yet,
though, is how to switch from one graphics mode to another. I tried simply
appending the following to the already written code, but that doesn't do
anything noticeable:


    LDA    #$E8        * load 1110 1000
    STA    VDGSET    * set pmode 3

Also: how to set the equivalent of SCREEN 1,0 / 1,1 commands?

This is my complete code so far:

TXTSCR    EQU    $0400     *Start of text screen
HIRES1    EQU    $E00    *Start of hi-res graphics screen
VDGSET    EQU    $FF22        *PIA1 data port B: VDG Control output
V0CLR    EQU    $FFC0        *Clear bit for Sam Chip (Graphics mode)
V1SET    EQU    $FFC3        *Set V1 bit in Sam Chip (Graphics mode)
V2SET    EQU    $FFC5        *set V2 bit in Sam Chip (Graphics mode)
F0CLR    EQU    $FFC6        *Display Offset Binary, This is the CLR Bit
(Video page offset)
F0SET    EQU    $FFC7
F1SET    EQU    $FFC9
F2SET    EQU    $FFCB
POLCAT    EQU    $A000        *Color Basic rom poll keyboard routine

    ORG    $7000
START    LDX    #HIRES1
    LDD    #$AAAA
LOOP1    STD     ,X++
    CMPX #HIRES1+$1800
    BCS     LOOP1
GMODE    STA    V0CLR    * set graphics mode
    STA    V1SET    * set graphics mode
    STA    V2SET    * set graphics mode
    LDA    #$F8    * load 1111 1000
    STA    F0SET    * set graphics mode
    STA    F1SET    * set graphics mode
    STA    F2SET    * set graphics mode
    STA    VDGSET    * set pmode 4 equivalent
    JMP    $ADFB    * wait for keypress
    LDA #$E8    * load 1110 1000
    STA    VDGSET    * set pmode 3 equivalent?
    JMP    $ADFB
    END START

Thanks for any input!

Cheers,
Fedor