Re: Crosspost: Did the cpu influence the display?

["Andrew Owen" <aoweninoz@yahoo.com.au>]

Bill H wrote:

> Relying on my memory and a cursory check on a number of websites it
> appears that the majority of Z80 cpu based computers had black and
> white displays, where as the majority of 65xx computers had a color
> display.

I must admit I can't think of a 6502 based machine that only had mono
graphics, but since all 65xx computers I'm aware of were designed for
home use (and hence games) a colour display would have been essential.
Most of the Z80 based machines were CP/M boxes designed for business
use and back then a colour display wasn't considered necessary for
serious applications. Except for the very early machines, all the Z80
based home computers I can think of had a colour display: Sinclair
Spectrum (Timex), Amstrad CPC, Tandy CoCo (Dragon), MSX etc.

> Now there are exceptions to this, but it makes me wonder, did the CPU
> influence the display?

Usually the display was handled by a video processor. Texas Instruments
made one that featured in most Z80 home computers in one form or
another. The ZX80 and ZX81 (TS1000) had no video processor and used the
CPU to generate the display. The Spectrum used a ULA (which wasn't as
powerful as the TI chip, but was probably a lot cheaper at the time).

> Is there an inherent reason why most Z80 computers had b/w displays and
> 65xx computers had color?

No. As a case in point I believe you can control all the screen modes
in the Commodore 128 using the Z80 rather than the 65xx. At the end of
the day a CPU is a CPU. You can connect anything you want to it (as
evidenced by the proliferation of IDE boards for both the Z80 and 65xx
machines).

> You may think it would have been cost, b&w would be cheaper than color,
> but in the majority Z80 computers where more expensive than 65xx
> computers.

That's the business vs's home thing again. Colour wasn't considered
necessary.

> Now it could have been display size, many Z80 computers used 80 columns
> which is hard to achieve when using a TV as a monitor. But on the other
> hand, with color you need more memory to achieve a good working
> resolution.

Many mono displays were text only (which is very memory efficient). In
fact even on colour computers like the Commodore 64 there was usually a
mono text mode available. Also a number of Z80 machines with a 512x192
display achieved 80 column text using a 6x8 font, which is just about
readable on a standard TV at that resolution.

> So the question is, did the cpu influence the display?

The answer is still no. In theory you could hook up a Z80 to a modern
display card and an IDE storage device and stream graphics to it (I
don't advise anyone to try it though).

P.S.

While we're on the subject of graphics I've seen it claimed that the
Commodore 64 can do an 8x1 attribute mode screen that is at least as
big as (possibly bigger than) the 256x192 (8x1 attribute) screen on the
Timex TS2068. But I can't find any reference to it in any of the online
C64 documentation. Is this a user mode (Using the CPU to change the
attribute byte in 320x200 mode for instance) or is it a hardware mode?
Also, if anyone from the other groups knows, can any other machines
manage something akin to this mode. I'm working on a project which will
use a 256x192 (8x1 attribute) screen mode, and if it is possible I'd
like to see it appearing on more than one 8-bit platform. (If you want
to kill the cross posts, just post it to comp.sys.sinclair).

Cheers!