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

[Timothe Litt]

On 23-Mar-20 13:35, Robert Armstrong wrote:
>> Timothe Litt <litt at ieee.org> wrote:
>> KS10 ... The 8085 code is crammed into UV EPROMs.
>   Was all of the KS CFE code in EPROM? 

Yes, it is.  There are a couple of microwords in the CRAM that deal with
console responses (single step, console interrupts for the serial
lines).  But that's it.

The KS can, and does initiate some bus cycles to get an RH11 tape or
disk to load a record into PDP-10 memory.  That record contains the CRAM
ucode.  The 8080 reads it from -10 memory and load the CRAM.  And once
it's a PDP-10, the next stage of boot (again, a few instructions) loads
the monitor bootstrap.

The CSL has no dedicated mass storage - and that was an issue of
reliability even more than cost.  The other issue is that CSL didn't
have a lot of space.  At the time, you wouldn't put DRAM on an 8085. 
(And if you did, you needed yet another few chips of refresh controller,
address decoders, etc.)  SRAMs were small and expensive.  And once you
took up the space for an EPROM socket, you might as well make it big
enough to hold everything...

One nice thing about the KS is that it was very well documented.  (Had
to do something with the time while internal politics prevented its
release before the 780...)  There's a copy of the technical manual on
bitsavers, which you can read for more entertainment.

>  On the 730 only a small kernel of 8085 code (about 2K as I remember) was in ROM/EPROM and the rest of the 8085 memory was RAM.  The first thing the 8085 did at power on was to load the rest of the 8085 code from the TU58.  That made it possible to issue updates to the CFE code as well as the microcode.
>
> Bob
>
>
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