Fwd: 4MB S100computers switch settings fro Cromemco

[cro memcos]

All,

So as the blurb in my listing says   INV012, Retro, 4MB (not KB) S100 computers Static Memory, S100 Buss Bus | eBay

I am reluctantly considering selling this 4MB card which I think could actually work in an XXU based system.

The card does not support Bank Select and so I'm sure it would not work on a Z80 or 68000 or 68010 cromemco system.

But on a 68020 system which expects only extended addressing?

The link for the card documentation is here

S100 Computers - 4MG RAM Card

Is there a consensus on what switch settings would be required  (3 banks of switches,  2 sets of jumper blocks, and one 4 way switch !!  ) for 

a) addressing 0 - 4MB

b) addressing 4-8 MB

My XXU system is just into storage,  but if everybody tells me the switch settings for above a) and b) are trivial I am minded to try and get it back, and test the card.

every hopeful,

marcus

[Richard Muse]

The card does work in DPU, XPU and XXU systems. The note below explains how to set the switches.  Sorry for the poor quality of the pictures.

Using the 4MB static ram board from John Monahan in a Cromemco Computer.

The picture of the 4MB board shows the correct jumper and switch settings
and the the picture of the 64FDC shows the jumper location on the 64FDC to pin 69.
This jumper will also work with a 16FDC. It was necessary to use S100 pin 69
for the RAM disable (instead of pin 67 - Phantom*) to allow the copy of RDOS
to ram on boot. Pin 67, the S-100 designated *Phantom line, is used on the
DPU, XPU and XXU and is labeled memdsb* but does not function as a Phantom*
line and asserts pin 67 all the time.

I used the S100 pin 69 on the 64FDC to pick up the ROM enable without
interference. This pin is labeled RFU3 on John's 4MB board, To utilize
this on the 4MB board, install a jumper on the lower pins 7 instead of
on 5 on P52 and open SW4,7 instead of SW4,5. I have found this to work
with the DPU, XPU and XXU.

This board is the first 4meg. Higher addressed boards do not, of course,
need the Phantom* line.

Richard M

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[curt mayer]

The xxu has a unique 32 bit access mode.  Has anybody ever documented it?

--curr

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[Peter Higgins]

The only documentation I am aware of comes from a short interview with one of the Cromemco engineers that appeared in an issue of S100 Journal (Fall 1986) in which this short explanation is provided:

"In a similar way [to the IEEE696 standard S100 signals sXTRQ and SIXTN]the XXU can request a 32-bit-wide transfer on the sMURQ* line (for Multiple ReQuest), defined as pin 69 of the S-100 bus. If the slave device is capable of 32-bit transfer, it responds with a MUAK* signal on pin 66 of the bus. The 32-bit transfer is then accomplished as two, rapid, successive 16-bit transfers in a single bus cycle. Using this technique, 32-bit data is transferred at an impressive rate of 8.33 megabytes per second on the S-100 bus. If the slave does not respond with MUAK*, then SIXTN* is checked and either 16-bit or 8-bit transfers are performed. This assures compatibility — although at lower transfer speeds — with IEEE-696 boards not capable of 32-bit transfers. (Editors note: Pins 66 and 69 are defined in the IEEE-696 standard as ‘Undefined’ and ‘Reserved for Future Use’ respectively. The signals sMURQ* and MUAK*, implemented by Cromemco, are not presently part of the standard)."

[Mike Stein]

Were any boards other than the 2048KZ capable of 32-bit transfer?

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[Peter Higgins]

On Monday, September 9, 2024 at 11:25:04 PM UTC-7 Mike Stein wrote:

Were any boards other than the 2048KZ capable of 32-bit transfer?

The only RAM board supporting this 32-bit transfer scheme was the Cromemco 2048KZ.

[Mike Stein]

I guess the 1024KZ was in between the 256KZ and the 2048KZ; no bank switching like the 256KZ but no 32-bit transfer like the 2048 either?

And the M series boards couldn't do 32-bit transfers but they had error correction?

Have I got that right?

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[Mike Loewen]

Could you be a little more specific on the pin 69 mod for the 64FDC? From pin 69 to where? The fuzzy picture doesn't help. I will soon be replacing a pair of 256KZ boards with a Dan Monahan 4MB SRAM board.

[Richard Muse]

The jumper is from S-100 pin 69 to IC-48 pin 8.

Richard

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[Mike Loewen]

Thank you. And, that should have been John Monahan, not Dan.  :-)