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

[Johnny Billquist]

On 2020-03-23 22:32, Clem Cole wrote:
> 
> 
> On Mon, Mar 23, 2020 at 3:57 PM Johnny Billquist <bqt at softjar.se 
> <mailto: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].    

Now that you say it, it rings a bell. I must totally be mixing the 750 
and 730 up...

> 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.

Looking a bit at the documentation, both the console and the TU58 are 
run directly by the VAX CPU. They are both just serial ports anyhow, so 
not much to do for either, actually.

The microcode is in ROM, so not loaded at all. But there was a bit of 
patch ram available to correct bugs in the microcode.

And NetBSD still have that microcode patch file in the distribution. It 
originally came with Ultrix, I believe. And if NetBSD boots on an 
11/750, it will patch the microcode. But I don't know what the patches 
actually fix. Maybe someone else knows...

Not sure if you could update the full microcode on the machine. I 
haven't seen anything suggesting it is possible in the documentation...

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol