[Coco] Looking for a Coco3
surtoutnombliepas at yahoo.ca
Wed Sep 13 08:53:34 EDT 2006
Thank you Phill for your help. It's why I expect to use a CPLD, to replace the TTLs and have the possibility to change the logic easily if I made a mistake.
Phill Harvey-Smith <afra at aurigae.demon.co.uk> a écrit :
Sylvain Rousseau wrote:
> I got a Coco3 again in 2002 and now I want to try to make a 512k
> upgrade kit for it using SRAM (not DRAM) and a CPLD but I'm afraid to
> burn it. So, I'm looking for a cheap Coco3 that don't need to look
> well but it should works. If my 512k SRAM upgrade kit works, I want
> to make it public via this CoCoList.
I can't help with the CoCo3 I'm afraid, however I am currently working
on a similar project for the Dragon 32/64 (and by extension should be
pretty easy to adapt for the CoCo 1, though poossibly trickier for the 2
as there where several different models :( ), to replace the 4116/4164
memory chips with a single 128Kx8 SRAM, as I have a whole bunch of them
that I got essentially free :)
The main problem that I have encounterted so far is that 4116 and 4164
chips have seperate data in and data out pins, the data in are connected
to the CPU bus, but the out are connected with a LS244 on the CPU side
and a LS373 on the VDG side, this should be easy enough to solve using
something like an LS245, with the data from the RAM being on the VDG
side and gated by E and R/W (or derivitives).
This of course may not be a problem for the CoCo 3 as the Gime may well
handle this. I know cirtain CoCo2 models had a special LS buffer chip to
do this and others did it via the 6847T.
You will of course also have to de-mux the row and column addresses, but
this should be pretty easy as you just need to latch one half on ras and
the other on cas which will give you the complete 16 bit address for
I'm about to make the board for this so I'll let people know how I get
on. Eventual hope is to implement a CoCo3/Dragon Beta like paged memory
system, using a small sram as a memory mapper (something like a 6116
should do the trick I figure).
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
"You can twist perceptions, but reality won't budge" -- Rush.
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