[Coco] Proto CoCo

Roger Merchberger zmerch-coco at 30below.com
Mon Aug 28 14:34:14 EDT 2006

Rumor has it that Gene Heskett may have mentioned these words:

>I can do the routing on my cnc micromill.  That shouldn't be more than 30
>lines of gcode to hand carve a working approximation of that edge profile.

That's one of the main things that's been stopping me from a pet project I 
started about 5 years ago... The other thing was drilling *all* those holes 
for a fair amount of TTL to do the buffering/latching/address decoding for.

>But I'm also partial to having the address decodeing and buffered bus stuff
>all present and accounted for.

Which is what I had started implementing...

>   Ditto OC buffers for all the IRQ related
>stuff so we don't see the IRQ's blinking the video slightly since there's
>way too many pullups using way too low R's in the average lashup.

This is what I'm less knowledgeable about.


What I'd originally wanted to design/build was a buffered bus "companion" - 
with a ROM socket, integrated latched I/O, *full* address decoding for 
several addresses, a small breadboard, and pin headers for wire-wrap access 
to the bus signals... and if I got way overproductive, maybe some built-in 
A/D\D/A to boot. Basically the "ultimate" hacker/experimenter board for the 

However, the board space for all the 6-bit/8-bit buffers & latches started 
taking up quite a bit of board space.

Now that the 16-bit buffer chips are out (and in surface-mount) (and I have 
access to some on some spare boards) the board would be much easier (read: 
less drilling) to build with a lot less board real estate consumed just for 
the primary support chips.

I also wanted to put the address decoding I felt was necessary into a 
PAL/GAL instead of diddling with individual AND/OR/NOR gates, but I'm 
obviously not smart enough to understand those critters; as there's no such 
thing as a "PALs/GALs for Dummies" book yet. I guess there's a reason for 
that. ;-)

I think I still have all the files WRT my project (and I even think I have 
the original (not complete) board artwork (done in AutoCad - it's all I 
know ;-) *somewhere*...

If I wasn't going 7:30 am -> 3:00 am maybe I'd have time to restart the 
project again... ;-)

BTW, is there any good all-around circuit software for Linux - *but* not a 
standard Linux distro? PCB compiled fine on my Linux From Scratch machine, 
but gEDA barfed horribly last time I tried to build it - in such a way that 
it confused me no end (no surprise there) and I gave up on it. I'd consider 
any halfway decent package, good libraries a plus but certainly not 
necessary (but bonus points to software that's especially easy to *make* 
part libraries).

Roger "Merch" Merchberger

Roger "Merch" Merchberger   | Anarchy doesn't scale well. -- Me
zmerch at 30below.com.         |
SysAdmin, Iceberg Computers

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