z80 timing... 6502 timing - test-drb@ccmp.vtda.org

19 Apr 1999

See my one comment embedded below, plz.

Dick

-----Original Message-----
From: Tony Duell &lt;ard(a)p850ug1.demon.co.uk&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Sunday, April 18, 1999 2:08 PM
Subject: Re: z80 timing... 6502 timing

...
 >
> I want to distance myself from the majority of this nonsense.  Building a
> simple computer with a processor, a ROM, a full compliment of RAM, and a
> serial console interface is a 10-minute design and a 90-minute fabrication
...

Less than that, actually. There's nothing to 'design' IMHO - just stick
the chips on a piece of wire-wrap board and wire-wrap the address and
data buses. While you're doing that, design the address decoder with the
other half of your brain.

I built a 6809 SBC years ago, and the chip count was pretty minimal.
IIRC:
6809 CPU + 4MHz crystal as the clock
2 off 6264 RAMs (16K RAM total)
2764 EPROM and space for a second one
6551 + MAX232 serial port
9914+75160+75162 GPIB port (that was in the spec, obviously not needed
for a general-purpose machine).
2 off 74LS138 address decoders (one to divide the memory map up into 8K
blocks, the other to subdivide one block for the I/O chips). These days
I'd use a GAL.
A couple of TTL latches and buffers for I/O ports (cofig switches, status
LEDs, etc).

That was it. Obviously a 6502 could be used with much the same hardware.
A Z80 wouldn't be any worse either. 

Rockwell made a 65C102 available in the same speed grades as the 65C02.
This used a quadrature clock just like the 6809 and worked pretty much like
it as well, at least insofar as the timing circuit was concerned.

...
   Now I
can't imagine why a graphics display, or anything so inane as that
 could creep into the consciousness of an otherwise perfectly sane person
 wishing to deal with one of life's fundamental mysteries, i.e. "which is
 really faster, the XXXX or the YYYY?" 
Oh, Sam was suggesting all sorts of complex features and I was pointing
out that most of them weren't that hard to add if you really wanted them.
You don't want them for this challenge IMHO.

-tony