S/23 machine update card

Guy Sotomayor Jr ggs at shiresoft.com
Mon Aug 19 11:15:24 CDT 2019

The uCode in the S/23 is 8085 assembly code that is contained within the ROMs.
The ROMs have the ability to be patched and the card you’re referencing is used to
hold those updates.  So without that card you’re not able to apply any ROM updates
(which are loaded each boot).

It’s been long enough that I don’t recall what (if any) updates there are and when (and
from what) they’re loaded.

The system architecture allows for *much* more than the 64KB normally accessible by
the 8085 CPU.  The memory is bank switched.  There is a fixed ROM and fix RAM portion
of the address space and a bank switched ROM and RAM portion of the address space.
16KB of fixed (for ROM/RAM) sticks in my head for some reason.  I don’t recall the
granularity of the bank switched areas.

There was a lot of confusion when the S/23 came out about what the ROM/RAM
specifications (192KB of ROM, 128KB of RAM) because an 8085 could only address
64KB.  ;-)

The patching was accomplished by having each major or critical function in the ROM 
be dispatched through a call table (that is placed in RAM at boot and can be “patched” 
to point to a different function).  It was *more* than just the ROM address as it also
contained the bank # of the ROM as well since (with few exceptions) all calls were
“long calls”.

TTFN - Guy

> On Aug 18, 2019, at 6:11 PM, Jon Elson via cctalk <cctalk at classiccmp.org> wrote:
> On 08/18/2019 06:38 PM, Dennis Boone via cctalk wrote:
>> Folks,
>> I've determined that the piece of my S/23 that's causing the power
>> supply to blow its 12V fuse is the machine update card.  The manual says
>> this provides additional R/W storage for microprogram updates.  That
>> sounds like something that wouldn't be necessary for normal operation.
> Not knowing anything about this system, but you might check the card for a bad Tantalum capacitor.
> Jon

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