Re: Homebrew STG card

[stratton-at-mdc.net]

> Another possibility is to encode all the logic, both ISA interface,
> digital I/O, and the encoder counters into a programmable gate
> array device.  Then, the entire board would consist of one big
> chip, like the Xilinx XC95160 and one or two A/D and D/A
> chips.

He's right about that... plus with canned PCI interface libraries
(using these chips is like writing C code) interfacing to that more
popular bus would no longer be unrealistic.  

Even with ISA, some programmable logic saves all the address decoders
and the like.  It would be wonderful to fold in those pricey encoder
chips.  The only thing I wonder about leaving discrete is an 8255 I/O
- they are cheap enough that it might be less expensive to keep that
external and generate a chip select for it and thus save 24 pins on
the gate array.  Of course toss more than one or two chips on the
board and it becomes necessary to buffer the bus - but maybe we
already have to essentially do that for the DAC's.

One big decision to make is if the LS7266 (encoder chip) register
structure should be copied, or replaced with something new.  I found
it a rather complicated programming model, but it worked fine once I
made sense of it.

Chris

-- 
Christopher C. Stratton, stratton-at-mdc.net
Instrument Maker, Horn Player & Engineer
30 Griswold Street, Cambridge, MA 02138
http://www.mdc.net/~stratton
(617) 492-3358 home/shop