Modifying microcode

Henk Gooijen henk.gooijen at
Wed May 30 10:43:41 CDT 2018

Van: Noel Chiappa via cctalk<mailto:cctalk at>
Verzonden: woensdag 30 mei 2018 15:51
Aan: cctalk at<mailto:cctalk at>
CC: jnc at<mailto:jnc at>
Onderwerp: Re: Modifying microcode

    > From: Kyle Owen

    > I do have an 11/45, though... so with this modification, I suppose one
    > could have some fun:

That's for the -11/40 - very different machine, one couldn't use the same
technique on the /45; the /40 is prepared to accept additional ucode on
additional CPU boards, that's how the EIA works:

And it's custom boards, the design for which is no longer extant (pity, as
I'd love to play with one myself).

Finally, I have this vague memory that they had to put a few minor mods on
some of the existing CPU boards (details also lost), although my memory may
be misleading me on that.


I am (way too slow) repairing an 11/35, and I am looking at the details
of the CPU, execute micro-stepping, etc. In that process I got the idea
to develop some “extended microcode patch” board … but forgot about
it, because I’d better get the 11/35 fixed first.
My findings so far :<>
Comments are very welcome!

As the EIS and FIS are extensions on the microcode, the hardware does
support microcode extensions.

The only two PDP-11 processor that have microcode extension options
are the 11/60 and the LSI-II (WCS).

Henk, PA8PDP

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