End 2022 I added the logic for the IBV11 – the GPIB interface in the MINC. But only the basic logic necessary to pass the VIBB test, and only really for the bragging rights, to be able to say that my MINC passed the chains on the XXDP22 and XXDP25 packs. After all, I didn’t have any instruments to connect to. But a short while after that, Jan Secker ran into a nice GPIB capable multimeter – a Philips PM2519, and he took up the challenge to extend the IBV11 to work with it.
A year or so passed – while I was mostly working on home improvement, and the subject of GPIB kind of slipped my mind. Until I suddenly got a mail from Jan saying he had it working! Besides the new ENC28J60 support, that’s the second major announcement for the upcoming new version that I’m in the process of finishing up: the MINC now has a fully working GPIB interface!
The logic has of course been tested with Jan’s PM2519, and meantime I’ve found myself a Philips PM6666 counter – and, it turned out that I had a GPIB capable instrument all along, my old HP 1640B Serial Analyzer. All three work as expected, and with every GPIB trick that they support – including things like serial poll. The one thing that we’ve not been able to test is if parallel polling works, and for a very simple reason: none of our instruments supports it.
Of course there’s a bit of wiring involved; GPIB has 16 signals, 8 for data and 8 for control. And a lot more physical wires even, because most of the control signals should be wired in a twisted pair with ground; the standard GPIB connector has 24 pins. Also there are voltage levels to be considered, since GPIB uses TTL levels and FPGAs usually have 3.3V I/Os at best. Jan designed the following interface:
which I made into a PCB with a GPIB connector on it – except that’ll need another redesign, because in the current form it is nice for debugging with lots of extra pin headers but also way too big at 100x80mm, and really awkward sticking out the back of an instrument, and even worse if it has to be upside down like on my HP 1640B. But hey, it works! and when I get around to the improved PCB design, I’ll share it here – along with lots of other MINC interface hardware that I’ve been working on!