newbie building a scratch-built computer

[Ensor]

Hi,

  >> Good point, and the exact reason I picked up a "Softy S3"
  >>about 10 years back (which is in SERIOUS need of TLC
  >>unfortunately).
  >
  > I rememebr seeing the adverts for that -- and drooling :-).

It is a *SERIOUSLY* useful device....it'll even emulate RAM, which is 
surprisingly useful when debugging code. :-)

  >....Alas I was an undergraduate at the time, and no way could
  >I afford one, so I built my own programmer/emulator....

I first came across the S3 in '89, it was standard equipment at the company 
I was working for at the time. It's one of the few times that I have been 
genuinely blown away by a piece of technology. A sort of "Eureka" moment.

Even then I couldn't afford (well, justify) the cost of getting one to use 
at home. In the end I picked this one up in '97, from the small ads of the 
local paper, for £35!

It had been dropped, so the case is pretty badly damaged, but other than 
needing an new Ni-Cad battery pack it's fully functional. Or at least it 
was, I seriously need to overhaul it.

The irony is, I'm pretty sure this unit is one of the very ones I used 
between '89 and '91. The guy I got it from bought it at a "clearout" sale at 
Aston Science Park in '91....which was when the aforementioned company I'd 
been working for, on said science park, closed down.... :-)

  >....3 large boards of TTL chips (I couldn't use a processor,
  >what could I have programmed the firmware with :-)).

LOL, good point.

I actually built my first EPROM burner from scratch too (though I never 
built an EPROM emulator). I had little choice, as an Atari user my options 
for off the shelf programmers were very limited - most connected via RS232, 
no use to me as I didn't have the 850 serial/printer interface module. And 
the only other one I remember would only work in an Atari 800 as it plugged 
into the right hand cartridge port (I, of course, had a 400).

So I threw together a very simple design which connected to the machine via 
it's joystick ports. The joystick ports were connected to a 6520 PIA inside 
the machine which gave me two 8 bit I/O ports to play with.

Used one port to pass the data to be burned, and used the other to provide 
assorted control signals - like the programming pulse, clocking/resetting a 
pair of 4040 counters which provided the address to the EPROM (I said it was 
simple), etc.

Worked surprisingly reliably.


  > I do have the original Softy somwhere. SC/MP based, TV output,
  >programs 2708s. I can't rememebr if it emulatrs as well.

I've never actually seen one of those for real, just pictures.

Is it just me, or did they use a very similar case to that of the ZX-80? 
Certainly, the bottom part of the case looks identical in the pictures I've 
seen.


  TTFN - Pete.