KD11-E/EA microcode flow diagrams

[Noel Chiappa]

    > From: Fritz Mueller

    >> the last microinstruction for RTI/RTT has been moved from 002 -> 744.

    > So what's at 002 now? Maybe something new was required there by micro
    > branch/fork logic, so the original contents had to be moved?

Well, it turns out I've been transcribing the ucode flow diagrams from the 34,
as part of a deeper look at the 34. (Dave B and I need a PDP-11 in the FPGA on
the QSIC, to run the USB protocol on; rather than using a microcontroller, we
decided the hack value of putting an -11 in there was too much to resist. It's
also practical, though - we're already very familiar with it, have a good
toolchain for it, etc. One option for that - we know about the existing FPGA
-11's - was cloning the /34.)

So according to that table:

  http://gunkies.org/wiki/KD11-E/EA_microcode

there is no uinst at 002 now! So I have no idea why they moved it. (The place
they moved it to, 0744, seems like it was the first empty location.)

There is a dump of the 34A microcode here:

  http://www.bitsavers.org/pdf/dec/pdp11/1134/m8266_ucode.out.txt

and for 002 it gives 

  Called by......... = IR or BUT only
  NEXT MPC.......... = 015

but 015 doesn't seem like a useful place to branch to? Maybe location 002 was
just abandoned (I have no idea why), and that's some leftover trash?


BTW, the engineering drawings contain three errors (fixed in the table above;
see the notes there), so I suspect they were drawn up by looking at a set of
the listings. I wonder if the actual source has survived? Probably not,
alas...

	Noel