Re: Crosspost: Did the cpu influence the display?

[bv@wjv.com (Bill Vermillion)]

In article <4DDF9231A0%news@youmustbejoking.demon.cu.invalid>,
Darren Salt  <news@youmustbejoking.demon.cu.invalid> wrote:
>I demand that Andrew Owen may or may not have written...
>
>> 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, [...]
>
>Acorn Atom, I think.
>
>>> 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.

>True. But the *layout* of the display memory was certainly
>influenced by the CPU. The Spectrum's screen memory is laid out
>to take advantage of register pairing when writing character
>bitmaps (increment the high byte to get to the next line within
>a character cell), and Acorn's 8-bit machines (at least the BBC
>and Electron) used a layout such that each character cell used a
>contiguous chunk of memory (8, 16 or 32 bytes, depending on the
>number of colours).

On two of my first machines the video really didn't have a lot of
processing.  There was a character generator chip and you wrote a
character to a memory spot and it displayed on the screen.  Pure
memory mapped without a lot of overhead like we saw on machines
that came along in 1979 and 1980.

-- 
Bill Vermillion - bv @ wjv . com