looking for 2100S microcode programming snippet

From: Jay West <jwest_at_classiccmp.org>
Date: Tue Mar 16 23:29:12 2004

Frank wrote...
> 105000 through 105377. You only get 7 bits to play with. And only bits
> 7-4 are used as bits 3-0 of the microcode ROM address.
>
> The lowest-numbered microcode ROM module, excluding module 0, is where
> the primary jump table lives (in the first 16 words).
>
> Is that what you're looking for?
Yes, but I must be missing something, it doesn't make sense to me. Is the
manual you're looking at for the A, or S? S has room for more modules.

According to docs I do have:
The 2100S has 1024 24-bit words of control store, divided into 4 modules of
256 24-bit words each. They are allocated as follows:

module 0 : 0-377 basic instruction set
module 1 : 400-777 IOP, FP, or User
module 2 : 1000-1377 FFP-1, or User
module 3 : 1400-1777 FFP-2, or User

The above is from a 2100 hp hardware repair manual, but it doesn't go into
macroinstruction address to microroutine address mapping and exactly how
that works.

That sounds like the range for all 4 possible modules is 0-1777, which also
jives with the same manual saying that bits 8-0 (9 bits) are for the
"address". I'm definitely missing something in my understanding. Probably
partially because I only have a 21mx microprogramming module and I'm trying
to make 2100 inferences from that. Where am I going astray? I guess I could
see how it is possible to use less bits than represent 1777 if you have a
jump table, but putting a jump table in whatever the lowest microcode module
is doesn't make sense to me, as the user can put different combinations of
modules in... I'm confused :\

> Yes, I oughta get around to post-processing the scans into a PDF.
I would like very much to see the relevant sections to the above concepts!

Thanks much!

Jay
Received on Tue Mar 16 2004 - 23:29:12 GMT