[GreenKeys] [External] Re: More BRPE progress: a schematic

[Jones, Douglas W]

From: Eric Moore <mooreericnyc at gmail.com> -- Friday, April 18, 2025 2:21 PM

> Hey Doug, my fully operational 8 bit BRPE and encoder is packed in a pelican case and ready to ship if it would be useful to you.

I'm a long way from needing a working BRPE.  We've got a 1965-vintage PDP8 that will eventually be able to drive the BRPE, but before that, we need to get the core memory working.  It hasn't worked at all until last Monday, when we got the first nonzero values out of memory that I've ever seen.

Once we get the core tuned up (we have the memory tuning instructions), the next order of business will be to toggle in simple programs from the front panel to see if the CPU basically works (we know a lot works because most of the data paths in the CPU are used when you toggle data into memory and then inspect it.

Once we get some simple programs running (like counting in binary), then we'll start trying to drive an ASR-33 at 110 baud, and only after we get that working will it be time to start working on the (significantly trashed) I/O option backplane that includes the paper-tape reader and punch controllers.  Only at that point will a working BRPE matter (we also have a Tally high-speed paper-tape reader).

Where the BRPE punch seems to be all about buckling knee-joint toggle linkages, the Tally Reader is all about differentials.  It has three of them, one driving each tape reel and one to drive the tape-advance sprocket wheel.  I photographed one of the Tally differentials to illustrate the Wikipedia page on differentials.

           Doug Jones