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Dual Pentium EISA SBC (Diversified Technology ESP3520)

L

legodude

Experienced Member
Joined
Oct 2, 2023
Messages
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I just picked up this SBC as it was too unusual for me to resist:

2025-03-03 20.52.32.jpg

Aside from a hit on The Retro Web, there is very little info available:

Diversified Technology (DTI) ESP3520B

Diversified Technology (DTI) ESP3520B is a motherboard based on the Intel 430NX (EISA PCIset NX Neptune) chipset. Get specs, BIOS, documentation and more!
theretroweb.com theretroweb.com

Their website (via Wayback) has nothing about this card.

As far as I can tell, it only has PS/2 and serial. I'm trying to find an EISA backplane to test it out.

Anyone know anything about this card or have a manual squirreled away somewhere?
 
While that SBC does have a PCI/EISA configured Intel 430NX chipset with the 82375SB PCI/EISA bus controller, that edge connector is most definitely not EISA, it is too long and has an extra tang on the back of the connector. It may be that the front part of the connector is EISA and the back extra part is the PCI bus, or it could be a jumbled mess of both.

Whatever backplane it is supposed to be used in most likely breaks out both PCI and EISA slots. You could try a generic EISA backplane, but I would try and validate as many signals and voltage rails as possible to make sure you don't smoke the SBC. This obviously wouldn't give you the PCI slots, but you could at least get an ISA video card potentially working to bring the board up.
 
There is very little information on EISA backplanes, but it looks to me like the connector would plug into this (EISA-only) backplane:
1741091607602.png

I certainly could be wrong though, and there is PCI as you suggest. I haven't seen a PCI/EISA backplane with the same connector that this board has.
The RTC will need replacement and/or a battery for sure.
 
I'd say you could try making your own backplane, but getting EISA slots these days is probably neigh impossible. That extra weird connector in the back makes it even more remote.

I suppose you could solder wires directly to the connector and break out a basic ISA slot and give the board power. It shouldn't be too difficult to work out where the power and ground pins are.
 
legodude said:
There is very little information on EISA backplanes, but it looks to me like the connector would plug into this (EISA-only) backplane:
View attachment 1296577

I certainly could be wrong though, and there is PCI as you suggest. I haven't seen a PCI/EISA backplane with the same connector that this board has.
The RTC will need replacement and/or a battery for sure.
Click to expand...

There is a similar looking backplane currently listed on eBay. I searched online for for a BP8T-EISA-02 manual without any luck. It would be interesting to find some details on how that backplane is wired up.

www.ebay.com

BP8T-EISA-02 8 SLOT PASSIVE BACKPLANE | eBay

Find many great new & used options and get the best deals for BP8T-EISA-02 8 SLOT PASSIVE BACKPLANE at the best online prices at eBay! Free shipping for many products!
www.ebay.com
 
EISA slots are not impossible to find, but the "bonus" connector might be. If this board was more integrated (network/video/disk), then I for sure would think about soldering wires.
I need at least four slots:
SBC
Video
Network
Disk
Sound (+/-)

There are at least two EISA backplanes on Ebay. The one linked above is a better form factor, but more expensive. The other is cheaper but 14 slots which is overkill.
 
The other EISA backplane listing on eBay is interesting in that it has a photo of the bottom side of the backplane. There are slot specific traces which are clearly visible fanning out from the extra connector on the CPU slot to the other slots. That explains what some of the pins are used for on the extra connector.

From a quick look at the EISA specification, each slot should have slot specific MREQx# (Master Request for slot x), MAKx# (Master Acknowledge for slot x), and AENx (Address Enable for slot x) signals. If there are 3 slot specific signals for each slot, and the CPU slot needs to support fanning out to 14 slots, that is at least 42 pins on the extra connector.

http://www.ece.ufrgs.br/~fetter/eng04476/datasheets/eisabook.pdf

www.ebay.com

14 Slot ISA PASSIVE Backplane Board BP14T-EISA | eBay

INCLUDES WHAT'S ON PICTURES ONLY, NO OTHERS.
www.ebay.com
 

Attachments

  • BP14T-EISA_Bottom.png
    BP14T-EISA_Bottom.png
    2.5 MB · Views: 11
legodude said:
EISA slots are not impossible to find, but the "bonus" connector might be. If this board was more integrated (network/video/disk), then I for sure would think about soldering wires.
I need at least four slots:
SBC
Video
Network
Disk
Sound (+/-)
Click to expand...

If you soldered wires to a prototype ISA card, you could plug that into an ISA backplane and get several slots. Or if you found a generic LPX ISA riser, you could solder to that and get several ISA slots. LPX risers are still pretty commonly available.

legodude said:
There are at least two EISA backplanes on Ebay. The one linked above is a better form factor, but more expensive. The other is cheaper but 14 slots which is overkill.
Click to expand...

Even though it's overkill, it's less than half the cost. That other backplane is going to be close to $200 once you factor in shipping, taxes and maybe customs duties.

With the 14 slot board, at least you get the slots, so you could desolder them from the board and lay out a new one of your own. Send it off to one of the Chinese fabs to have it made.
 
The connectors are available for surprisingly cheap:
www.ebay.com

646039-1 AMP EISA STANDARD EDGE CONNECTOR 188 POSITION ( Qty 5 ) *** New *** | eBay

188 POSITION. STANDARD EDGE CONNECTOR. Condition: NEW.
www.ebay.com

My main problem with the 14 slot board is finding a case for it. The AT backplane I can get into a smallish case (or my Dolch 64). The large backplane limits those options (unless it runs into a saw, which I have also thought about).
 
The problem with cutting it down is it looks like the last slot in the bus has provisions for termination resistors that are notably absent. Also absent is something that goes in the "ISAAEN" sockets. Not sure if that's for another resistor network, filter or buffer chip.
 
Great point about the termination resistors. I wonder if those are required, or only needed if there are problems on the bus.

Re: ISA AEN, I found this from an unrelated topic and I assume it is the same general purpose:
1741304602390.png
 
I don't know much about the EISA spec, but the ISA bus was originally only intended to drive 6 or 7 slots at most. I'd imagine a faster and wider bus is going to have more problems with signal integrity on double the number of slots it was designed to work with.
 
For sure. The 8 slot EISA board on Ebay also has provisions for termination resistors. I looked at some ISA backplanes and some 8 slot boards also have space for resistors (some have resistors installed):

1741306853554.png
 
If you could figure out a source for that weird stub connector, you could roll your own backplane, since you found a source for EISA slots.
 
yeah, I'd probably want a real backplane to trace out the connections for the stub as I haven't been able to find really any documentation at all related to EISA SBCs/backplanes
I'd probably have to plumb the AMP catalog to try and find out what that connector is... or buy a real backplane and read the part number off.

My ebay offers are ongoing
 
Maybe you can come up with a cock and bull story to ask the seller to take a picture of the side of the connector "to check for compatibility with my SBC".
 
I ended up getting one of the EISA backplanes from Ebay and tried it out... No video using an EISA VGA card, then I remembered I had a POST card. It stops with errors B0 and AE, which seem to mean "check for errors" and "clear boot flag" respectively. I also dumped the Phoenix Bios and it seems to be reasonable-ish:


Code: 
TRW BIOS analyze (!b):
__________________________________________________________
File:     esp3250.bin
Vendor:   Phoenix
Version:  4.03
String:   
Sign-on:  ESP3520 Rls. 1.7
Metadata: [Build] DEVEL011
                  09/01/95 11:21:42
          [ID] PhoenixBIOS Version 4.03
               Copyright 1987-1993 Phoenix Technologies Ltd.
               Copyright 1995, Diversified Technology, Inc.
               All Rights Reserved.
          [Table] INTEL 82C430LX (System)
ROMs:


I can't really parse what these errors mean. I get the same error whether or not the VGA card is inserted.

I tried swapping the CPU - it won't boot with the CPU in the top socket only.
 
Yup. I've thought about picking one up, but given that the behavior does not change with the video card inserted or not, I wasn't sure if it was worth it
 
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