Re: WANTED: Apple III info

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

In article <16FEB199513502941@vax2.concordia.ca>,
Mitchell Spector <spector@vax2.concordia.ca> wrote:
> David Empson wrote: 
> >Yes - there are two bytes per character.  One contains the ASCII code,
> >the other contains two four bit fields for the foreground and
> >background colours.  There are no restrictions about colour usage or
> >placement.
> 
> 	I'm curious, why wasn't the Apple IIgs designed to be less 
> limited with text foreground/background color?

It would have been difficult to integrate into the existing text
screen without allocating at least one more soft-switch.  I don't
think a coloured 40-column text mode is particularly useful (e.g. for
ANSI implementation).  Colour 80-column mode would be better, but
would have required twice as much RAM.

> Or was this another case of of usual > absolutely-no-reason-for-such-
> and-such-a-feature-not-being-present?  (ie, 64k DOC RAM, lack of
> extra DMA pin, mono-out jack, 16 colors per scanline, etc, etc :|). 

64k DOC RAM: save money, design complexity and board space
extra DMA pin (i.e. three ROW selects): short-sightedness
mono output: significant saving in chippery in the sound circuitry
16 colours per scan line: pass

> >Not surprising - the III is intended to work with a Digital RGB
> >monitor, and is supposed to have a resistor network to produce analogue
> >weighting for an Analog RGB montior.
> 
> 	Does this mean it's _safe_ to connect an Analog RGB monitor to
> the Apple III's video port?

I wouldn't try it. The pinouts are almost identical, but the III is
feeding TTL levels into the monitor, which might be out of range for
the analog RGB monitor.  I can't be sure of this, without having a
closer look at the resistor network and ratings of the various devices.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand