21 Nov
2006
21 Nov
'06
10:51 a.m.
From: "Don North" <ak6dn at mindspring.com>
Vincent Slyngstad wrote:
Hmm...BGA...ick :-). We only need about 40 pins for this application.
Does anyone make a device with a smaller pincount? A nice solderable
64-pin qfp perhaps?
One of the questions I have kicking around (I
even bought an XESS
board) was: How hard would it be to get a PDP-8 core into an FPGA
and arrange the pinout to correspond to the 6100 or 6120?
Then it wouldn't be necessary to desolder 6120's from Decmates to
get our SBC6120's working :-).
Getting the logical signals to match would not be that big a deal; the
larger problem would be getting a compatible form factor. I retargeted
my PDP8 above to a XC2S30 and it occupies about 75% of the device. In
a CS144 (small 0.8mm pitch BGA) one could probably make a DIP40 plugin
carrier that was pin compatible to either the 6100 or 6120 parts. None of these devices use 5V supplies, they are all
1.8V~3.3V at most.
The power supply issue can be solved by a small linear regulator, but
I/O level compatibility is a stickier problem.
I was thinking a 3.3v device with resistors in the input paths to keep
them within range. The outputs would probably be acceptable as-is.
Anyway, it is an interesting problem, probably
solvable given more
thought and research. However, I suspect any low volume solution
will still be more costly than just tracking down old IM6100 ICs
for $10-$20. Not nearly as much fun, tho.
True, but figuring out how to one-off a replacement for a 6120 seems
a worthy project. Also, I think the cost-benefit equation will
continue to shift, as old parts get more expensive, and new ones
(hopefully) don't :-).
Vince