On Thu, Dec 3, 2015 at 2:24 PM, Josh Dersch <dersc...@gmail.com> wrote: > > My understanding is that 6015 does modify the accumulator -- from the > manual > ( > > http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/fabritek/402-1001-00_MP12refMan_1974.pdf > ) > Function code 5(8) is interpreted as "...if th the addressed device is > DONE, the next instruction in sequence is skipped, the contents of the > device buffer are inclusive OR'd with the accumulator, and the result is > retained in the accumulator..." > > So 6015 reads the next 8-bit quantity from the paper tape and ORs it onto > AC. >
Yes, it might very well. I wrote up a bit of code to test it out and don't remember that being the case, but then again, it was late and I was probably not thinking clearly. Yeah, I was actually just looking at that again and the jump to 7755 is > rather odd. I think that's what stumped me a couple of years back and > since I never got around to building the interface... I think I just > assumed a couple of bits had gone south on my PROMs, to be honest. > Well, fear not for bad bits, unless three of these units have failing PROMs. I think the ones in my colleague's unit are from the 1990s. Impressive they were using these units up until then (or considerably after, perhaps!). That's interesting -- on my MP-12, the sync interface brings out (IIRC) > three lines: clock, data in, and data out. I'd be interested to know what > hardware's hooked up to yours to provide all the goodies you have. > Indeed. All of the functions mentioned are all transferred via the synchronous interface. I'm not sure how much decoding is done in the big box versus the little box, but if I were a betting man, I'd say it's mostly done in the big box. The little box has the seven 7-segment displays, a paper tape reader, some arbitrary outputs, and some buttons. There are three removable cards to make it all happen, and the DA-15 connector supplies 120VAC as well as the synchronous data/clock lines to the little box. There's an effort to reverse engineer the little box, then move up to the big box. My colleague has already reverse engineered the 7-segment driver board. It's my goal to get all of this information collected together somewhere where it can be made available to all. I think the size and surprising capability of the Fabritek makes it the most clone-able of the TTL PDP-8s; much of the functionality of a Straight-8 for instance, without the bulk. If we went with surface-mount 7400-series, as well as battery-backed SRAM, there's a good chance we could improve upon the functionality (especially front panel operations!) and add more memory, switchable ROM space, etc. It'll be a pipe dream for now, though. Kyle
