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

[Toby Thain]

On 2020-03-23 5:49 PM, Ray Jewhurst wrote:
> 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. 
> 

Here's a decent start:
https://people.cs.clemson.edu/~mark/uprog.html

--Toby


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