Pete Hufnagel <CaptnZilog@aol.com> wrote:
> FYI, yes, the 780 does have writable control store.  At least, its listed 
> (and drawn) in the schematics...  from memory, I'm pretty sure it was not 
> just an option... but I could be wrong.   Not sure if the WCS was loaded fr
> the LSI-11 front end or whether it was loaded by the OS once running...  

Allison J Parent <allisonp@world.std.com> wrote:
> Exactly the use.  Proms of the time were too slow fo rhte numebr needed and 
> uCode was a bit unstable and tuneable as well so making it writeable was
> a good fix but not cheap.
> 
> The 700 series in general use writeable ucode stores (780, 782, 785, 
> 750 and 730 to be sure I may have missed a few).

The question wasn't whether the 780 had WCS, it was whether the 785 had
it.

According to the 1981-82 VAX Hardware Handbook, the 780 has 4K*99 of
non-writable control store, and 2K*99 of Writable Diagnostic Control
Store (WDCS).  The former is in PROM; the latter is SRAM but is not
(officially) available for user-written microcode.  The KU780 option
added another 2K*99 of writable control store, which could either be
used for the KE780 (G & H floating point) or for user microcode, but
not both.

The 725/730 and 750 use writable control store but do not support
user-written microcode.

The 785 has 8K*99 of writable control store.

I still would like to get a copy of the DEC software tools that
were sold for customer microcode development for the KU780, or at
least the documentation for them.  I don't know the title of the
software package, or whether it was sold separately from the KU780.