Modifying microcode

[Camiel Vanderhoeven]

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 classiccmp.org on behalf of cctalk at classiccmp.org> wrote:

    Has anyone attempted to reassemble and update the microcode on a MicroVAX?
    
    Seems like there's enough stuff here to possibly do it:
    http://simh.trailing-edge.com/semi/ucode/
    
    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, though...so
    with this modification, I suppose one could have some fun:
    http://repository.cmu.edu/cgi/viewcontent.cgi?article=3241&context=compsci
    
    Thanks,
    
    Kyle