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BUYER BEWARE -- SALOTA 32K Mixed Memory Boards

glitch

glitch

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I recently picked up a SALOTA 32K Mixed Memory board in unpopulated form from eBay through a seller in Germany. The board arrived just fine, with a copy of a CD that includes photos and schematics for a few SALOTA products. The mixed memory board is supposed to accomodate 2716 EPROMs and 6116 SRAMs on a neat S-100 card that includes an option for onboard or external battery backup for the SRAMs -- a jumper above each memory socket lets you select if you want to power the device from battery-backed or regular supply.

Well, I got around to building mine today, and all was going well until I replaced the 2716 EPROM with a 6116 SRAM. The board wouldn't write to it. After jumping the /WR line driver, I did get the board to write, but it was erratic. Furthermore, you could write on any 2K boundary and the information would end up on the first device (I started with only one memory device socket populated). After a bit of probing, I found out that these boards are defective! The /CE and /OE lines are switched, which means that the board works perfectly with EPROMs, but not so well with SRAMs.

It's possible to cut traces and sort this out, which I have done with my board (I'll post a guide later, if anyone is interested). It works perfectly once you do that, but it involves running 32 jumpers and cutting a bunch of traces (mostly on the back of the board, thankfully). I'm going to contact the seller and let him know, as I doubt he has any clue. He probably ended up with a pile of unpopulated boards because someone at SALOTA realized the mistake!

Now, the real question is, are these more valuable because they're unassembled defects apparently produced in quantity? :D
 
Maybe these signals are swapped on their CPU board? I have another s-100 bus computer that is not s-100 compatible some manufacturers seem to use the bus for their own purposes and are not IEEE-696 adherent.
Kipp
 
kyeakel said:
Maybe these signals are swapped on their CPU board? I have another s-100 bus computer that is not s-100 compatible some manufacturers seem to use the bus for their own purposes and are not IEEE-696 adherent.
Click to expand...

I'd thought of this at first, but the /CE lines and bussed together for the memory devices, while the /OE lines are selected via a 74LS154 1-of-16 decoder. Thus, you could never correctly select a JEDEC compatible memory device using this scheme (it works for EPROMs, but it's a kludge). So, all chips are always selected, and when you do a memory write, the /WR pin on all devices is pulsed. One device will also have its /OE line pulled low by the 74LS154, which I suppose results in bus contention -- likely the source of the inconsistent errors seen.

Also, SALOTA's Z80 S-100 processor board is apparently a (licensed?) 1:1 clone of the NorthStar Z80 board, so while not IEEE-696 compliant, their memory board should be S-1000 compatible.

Carlsson's explanation would actually make sense...does anyone know of a 2K x 8 SRAM that isn't JEDEC compatible but is close enough?
 
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Hi
While this won't help current owners of the SALOTA board, we do have a bunch of the S-100 EPROM boards left in case anyone needs an EPROM board for their restoration. They can be expanded up to 2MB of SRAM or Flash, EPROM etc. It also supports the smaller EPROMs for booting, etc.

It is a second generation board and doesn't require any cuts/jumpers/patches, etc. Please contact me if interested. Thanks

Andrew Lynch
 
lynchaj said:
While this won't help current owners of the SALOTA board, we do have a bunch of the S-100 EPROM boards left in case anyone needs an EPROM board for their restoration. They can be expanded up to 2MB of SRAM or Flash, EPROM etc. It also supports the smaller EPROMs for booting, etc.
Click to expand...

Indeed, if you need a mixed memory board and don't have a reason for wanting to use many 2716/6116 devices, the S100Computers/N8VEM board is definitely the way to go! I went with the SALOTA board because I wanted to use it with my Dajen SCI as a test bench machine, and the SCI doesn't assert /PHANTOM, so you have to keep your RAM out of its ROM space. Adding /PHANTOM would be trivial, but I'd rather not modify the board.

Well, it seems there /is/ an almost-JEDEC SRAM that will more or less work with this board -- the Toshiba TC5516. It has two /CE lines instead of /OE and /CE, and it uses /WR as RD//WR. I don't think this is what the designers at SALOTA intended, because the schematic is clearly labeled with /CS and /CE and the /WR line isn't set up for a strictly RD//WR use (it seems that it would work as such, but I don't believe MWRITE is guaranteed to indicate a memory read when false). I'm inclined to go with "it's a bug."
 
Thanks for this heads-up. I also bought one of these more than a year ago, probably the same source, but hadn't got around to building it yet. I held off building it once the N8VEM board project got moving. Then my 64k DRAM board got resurrected and I shelved it.

I would certainly appreciate any documentation of your experience and solution. Depending on the cost/benefit and time involved, I'll either go ahead with a build (some day) or cannibalise the board for some other project..

Rick
 
I'll do a write-up on the SALOTA board and the modifications necessary to make it JEDEC compliant. It's not too difficult...bit of track cutting, but you can bus some of the pins together with a single long piece of wire-wrap wire (as long as you have Kynar insulated wire, and don't mind melting through the insulation). I've been using the board since discovering the problem, and it's worked flawlessly so far.
 
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