16 Aug
2006
16 Aug
'06
3:48 p.m.
Tony Duell wrote:
Unless either (a) the USB part number is just their code for a standard
device (HP were fond of doing this...), or (b) you can disable the
internal mask ROM and run it from external program store, say by changing
the state of a pin.
Without knowing more about the device I can't possibly know if either of
these is the case.
TI realized early on that to make the DSP more ubiquitous, they
needed to suppport masked parts. Particularly for this sort of
application. I would suspect this is a low end 32010-ish part (?)
The CoCo 3 is designed round a custom chip called GIME (Graphics,
Interrupts, Memroy Enhancement). It handles all the video side, the
memory mamangement (remmber the 6809 can only directly address 64K), etc.
Said chip outputs a 9 bit multiplexed address (designed to link to the 9
addres pins on 256K bit DRAMs), and the DRAM timing signals. It also
expects 16 bit wide memory IIRC.
Ah, OK.
a TI/USR DSP chip, which is prolly useless outside of
the intended use
Some of the DSP's are "general purpose" -- external
program
store. However, since you called it a "TI/USR" part, I assume
it has a USR house number on it and, as such, is probably
a masked part. If so, "useless outside of the intended use" :> So, *if* I can get a Dynamic-RAM -> Static RAM
converter board designed
for the CoCo, I could upgrade 4 CoCo3s to 512K with each modem board.
What's
the issue *preventing* this from happening?
(unfamiliar with the internals of a CoCo3) It's probably possible to add external circuitry
to turn that back into a
normal 18 bit address and hang SRAM off it, but I think it's more work
than finding some 41256s...
I would assume the controller would exploit page mode references
(especially when dealing with sequential accesses like video).
If so, this muddies any attempt to convert multiplexed
addresses back to a form suitable for SRAM (unless you use
SRAMs that also support page mode access!)
Yes, assuming it produces an 18bit (9R+9C) address, 41256's
would be the right way to go.