Modifying microcode

Camiel Vanderhoeven camiel.vanderhoeven at
Wed May 30 09:34:26 CDT 2018

The microcode for the MicroVAX 2 (for which the MICRO2 assembler was used) and the CVAX (which is the CPU in your 3800) is implemented as a mask ROM on the CPU chip itself. No way to change it, and no way you can use MICRO2 to assemble the microcode for the CVAX.

On 5/30/18, 3:19 PM, "cctalk on behalf of Kyle Owen via cctalk" <cctalk-bounces at on behalf of cctalk at> wrote:

    Has anyone attempted to reassemble and update the microcode on a MicroVAX?
    Seems like there's enough stuff here to possibly do it:
    I'm thinking about trying to find a microcoded architecture to play with
    before I design something around the Intel 3000 series.
    I've got a MicroVAX 3800, so I suppose I could run MICRO2 to assemble the
    aforementioned microcode. But then what? I assume PALs would have to be
    burned to implement the new microcode. Or is it more complicated than that?
    I don't have a PDP-11/60, unfortunately. I do have an 11/45,
    with this modification, I suppose one could have some fun:

More information about the cctech mailing list