22 Sep
2023
22 Sep
'23
6:03 p.m.
On Sep 22, 2023, at 12:04 PM, Mike Katz via cctalk
<cctalk(a)classiccmp.org> wrote:
I'm working on the design for an Omnibus (PDP-8/E) debug board and I am not very good
at circuit design. I know there are programs that will compile something that looks like
C into Verilog/VHDL/Abel/Etc for use on some kind of large (more than 64 pins)
programmable logic device.
Can any of you recommend a good C like tool for programmable logic?
Thank you,
Mike
Spartan 2 FPGAs have (among other things) 3.3 volt output drivers, with a minimum high
output spec of 2.4 volts. That's probably good enough to drive 5 volt TTL devices.
(FWIW, I've had good luck driving 5V logic from the 3.3 volt I/O of a Raspberry Pico.
Not quite the same but similar). They also show 5 volt tolerant inputs, so while the
device is powered by 3.3 volt it can accept 5V TTL inputs without complaint.
I recently built a device that had a lot of inputs to that Raspberry Pico, which is
documented as NOT 5V tolerant. So instead of searching for level shifters I simply used
an array of resistive voltage dividers. Worked flawlessly.
As for a C like tool, I've heard of something called "System C" for logic
design. No idea if it is reality for any FPGA, let alone for the older ones. The
difficulty is that C is a sequential system description, which is fine for (single core)
computers. But logic such as FPGAs does many things concurrently, and that calls for a
different way of describing what you need. I'd suggest learning VHDL; it isn't
all that hard. Or Verilog I suppose, which I don't know. Years ago I bought Peter
Ashenden's "Designer's guide to VHDL" which is very good.
paul