[Coco] Coco Digest, Vol 122, Issue 19

[Sandro Mestre]

Oh, thanks! This is awesome. :)

2013/3/9 Brett Gordon <beretta42 at gmail.com>

> > Hello, I'm new to this list.
> >
> > I would like to code a game for the Coco1/2. I usually code for the
> > commodore c64 so I am aquainted with the 6502 but I also can code for the
> > motorolas 6800, 6809 and 680000. During the last days I have coded a
> sprite
> > engine for a computer with a 6809E and it is working great and then I
> > thought that I could code also the game for the Coco/Dragon computers.
> >
> > I need to know if there is a register that I can poll to check the
> current
> > raster position or if there is another way to know when the VDP starts
> > painting the horizontal borders. I am asking this because as many will
> know
> > if I paint the sprites there(borders) there will be no flickering.
> Another
> > option I have would be to use double buffering but then this would eat
> much
> > more memory and that would be perhaps a no go.
> >
> > How safe is it to use the high speed poke on a game? Do coco games use
> it?
> >
> > Thanks
> >
> > Wood
>
> Welcome Wood!  We need good programmers for the CoCo!  I have a
> feeling there is going to be some new hardware on the CoCo's horizon,
> and we need people producing new software.
>
> Unfortunately, unlike more sophisticated systems, the CoCo's VDG chip
> doesn't include an external register for scan lines; It does, however,
> send it's HSYNC and VSYNC lines to the PIA chips for Interrupt
> latching.   The HSYNC is latched and gated vi PIA to the FIRQ line and
> the VSYNC is gated and latched to the IRQ line.   You can setup the
> interrupts like this
>
> .db      scanline      ;;  scan line counter
>
> FIRQ:
>             lda    PIADATA       ;  clear pia interrupt
>             inc    scanline        ;  increment scanline on HSYNC (
> ~15,750 Hz)
>             rti                           ;  return
>
> IRQ:
>             lda    PIADATA       ; clear pia interrupt
>             clr     scanline        ; reset scanline counter on VSYNC (~60
> Hz)
>             rti                           ; return
>
> initirq:
>             orcc  #0x50            ; shut off interrupts
>             ldd    FIRQ              ; set BASIC's revectored FIRQ
>             std    0x103
>             ldd    IRQ                 ; set BASIC's revectored IRQ
>             std    0x106
>             andcc #0xaf           ; turn on interrupts
>             rts
>
> Double check usual places for the exact addresses for the PIA
> addresses, BASIC's IRQ handler addresses, and CC's INT masks :)
>
> https://sites.google.com/a/aaronwolfe.com/cococoding/
>
> is Aaron's great repo for technical docs on BASIC and CoCo in general.
>
> Cheers,
>
> --
> Brett M. Gordon, (CoCoBoot)
> beretta42 at gmail.com
>
> --
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>