Re: Apple ][gs VGA Card

[dempson@actrix.gen.nz (David Empson)]

In article <35felj$5s1@blackice.winternet.com>,
Dave Roberts <daver@drift.winternet.com> wrote:
> Nathan Mates (nathan@cco.caltech.edu) wrote:
> :    Ummm. From what I've heard, it's an 80186 on board.

It is an NEC V30, which has the instruction set of the 80186, with a
16-bit data bus, but different (faster) instruction timings.  The
PCT's V30 is running at about 7 MHz, but it is more like the speed of
a 12 MHz 8088.

> : Plus, don't
> : existing PCT users have to jump through hoops and drive cables all
> : over just to get the video to work. I think that the PCT board handles
> : all of the EGA graphics onboard, and it's be more of a hack than I'd
> : like to consider (I don't have one btw, and am NOT offering to learn
> : 80186 asm and try and support such a beast)...
> 
> 	Yep. I have one, and there are at least 5 or 6 cables running around
> to support it, along with an extra card to handle switching between video
> modes.

You're exaggerating a little, there.  In a IIgs, the PCT needs two
cables: disk drive connector (19 pin) and cable to the ColorSwitch
card (10 way), which switches between IIgs RGB video output and PCT
video.  The IIgs video output is connected to the ColorSwitch card,
and the monitor plugs into the card as well.

In a IIe, you also need a keyboard cable, a different video cable (two
wire), and a speaker cable (the speaker is routed through the PCT).

In either case, there are optional cables for a digital RGB monitor
(CGA compatible) and genuine PC keyboard.

> BTW, the processor is actually a Z80 (?), and the graphics are CGA,
> not EGA, though they could have easily done EGA on the GS monitor.

No they couldn't.  The IIgs monitor cannot handle the highest
resolution modes in EGA (350 lines).  It could do the lower resolution
modes with more colours than CGA, though.

I don't think it is feasible to use the Second Sight card for PCT
video output.  You would need to emulate the video RAM off-card, and I
don't think this is possible.  You would also need to implement a VGA
bios (without any additional memory being available on the PCT to
store it anywhere), and VGA "portware" functions loaded into AEPC.SYSTEM.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand