1 Oct
2001
1 Oct
'01
10:51 a.m.
Tony Duell skrev:
> Tony Duell skrev:
>
> >As I've said a couple of times before, I can make a video circuit with
> >somewhat better capabilities than the ZX81's built-in video (40*25 text,
> >block grapghics, colour) in 2 or 3 chips. Add another chip or so to
> >encode the outputs to PAL (although I'd probably prefer to feed the RGB
> >signals into a TV's SCART socket these days...)
>
> What chips would you use? I assume that the Speccy uses one chip for its
> entire video generation, but where would you split the functions?
I should have said _standard_ chips. Once you start
allowing ULAs (as the
ZX81, Spectrum, Oric, etc all used) then it's easy to do video in a
couple of chips.
Of course I don't expect you to be making your own ULAs. =)
I just wondered if you'd take some off-the-shelf VDU controller or something a
bit more open-ended.
Didn't we go through this a couple of weeks back?
The 2 chips I would
start with are an SAA5243 Teletext display chip (or an SAA5245 for the
States) and an 8K*8 static RAM (6264). You need to get a 6MHz clock from
somewhere (maybe another chip for that, if you can't also use it for the
CPU clock in some way) and maybe you want to buffer the video output lines.
Teletext? That's a funny idea.
> (update a few minutes later, aren't off-line
readers a wonderful thing?)
> I went and opened up my own seemingly-dead Spectrum... Wait, that's no ZX=
> 81.
> I've been thinking about SZ Spectrums all the time.
> Oh well, I might just ask anyway, since I've opened it up...
> What is that chip next to the Z80? It's labelled PCF1306P.
If it's another 40 pin chip, then that's the
custom ULA chip that
includes most of the glue logic.
Is that like a lot of 74138s or something?
> And why is there a switch glued on top of the Z80
with wires going to the
> character ROM? Since it's a localised character ROM piggybacked on top of=
> the
> one soldered to the motherboard, could it be for switching charsets?
Does the Spectrum really have a separate character
generator ROM. Doesn't
sound right to me...
I wouldn't know, but this is the chip which somehow enables Swedish
characters. Is it a patched BASIC ROM?
--
En ligne avec Thor 2.6a.
The most useful program will be continually improved until it is useless.