[Simh] Is it possible to simulate the first Vaxen I ever used?

[Ray Jewhurst]

Slightly off topic, could someone explain more about what microcode is and
how it works? The fact that the CPU instructions are they themselves
programmed in seems unfathomable.

Ray

On Mon, Mar 23, 2020, 5:33 PM Clem Cole <clemc at ccc.com> wrote:

>
>
> On Mon, Mar 23, 2020 at 3:57 PM Johnny Billquist <bqt at softjar.se> wrote:
>
>> The VAX-11/750 used 2901 though...
>>
> 750 was made out of custom CMOS gate arrays.  The main adder was analyzed
> as part of my thesis [long story - not for here, but a very clever
> circuit.  I would later get to know the guy that did it].     Paul Gilbeau
> and Dick Monroe were the main microcoders on the 750.  I'm pretty sure that
> Paul was also one of the 780 microcode folks.   Very interesting guy. I
> used to say he had a worm's eye view of the world -- perfect for his job as
> lead microcoder; but trying to get up a level could be difficult.  I've
> lost track of them both, although I still talk to Dave Cane a couple of
> times a year and I think he knows how to find most of the HW team.
>
> I'm fairly sure that the 750 used te BLISS based Micro2 tools as Tim
> suggested and as I said, we cloned them at Masscomp in C (which later it
> went west). Tim, you tell me, I thought the Masscomp version got sent to
> the Jupiter team, but I'm pretty sure it was used for Prism.  I remember us
> getting a 'bug report' because VAX-11/C didn't like something BSD's yacc
> had generated at one of the Hatfield/McCoy parties. I remember changing
> what it was and email it the next day.
>
> FWIW:   All of the Masscomp FP/AP and the DACP used that set of microcode
> tools since they were all AMD 29xx based.   IIRC, Chuck Palmer overhauled
> the original hack we did for Paul and Dick because a few Masscomp
> customers wanted to write custom DACP microcode and originally it was not
> too easy.   I probably have a manual for that still around and maybe even
> the tools. But, since I don't have a DACP on the MC500 I still have,  I
> never bother scooping up the tools.
>
> Also, I know that there was an Intel 808x processor (85 I think) that
> shipped in the 750, but it was not an FEP.  It was limited to running the
> cartridge tape controller.  I don't remember how the console serial port
> was done (the 780 it was part of the FEP).  The 750 microcode did the boot
> as someone else pointed out.  I've forgotten how the microcode was loaded
> on a cold start.   I thought there was something in a ROM/EPROM, but I've
> forgotten.  I do know the cartridge tape unit was needed to update the
> microcode and that was the only way to do it.  But I don't remember you
> need to have the tape on a cold reboot the like floppies on a 780, but I
> could have forgotten.
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