Re: [N8VEM-S100:7434] Re: 16mb SRAM Version 03 Board Success!

[Gary Kaufman <geka...@gmail.com>]

David -

Thanks for the confirmation of the jumpers, I do have them correct.  At one point I left off P3 (intentionally) and ran it as a 8mb board - I seem to recall that it was far more reliable that way, although I have no idea why that might be.

In any case, this board was frustrating me for a long time - the 4mbx8's were expensive and the board is very cosmetically attractive so I really wanted to use it in the system.  Glad to have it finally working nicely.  For those in the USA, Unicorn Electronics has both 74F240 and 74F139/74S139 at $0.49 each.

I have the V5 board waiting to construct, but will probably just recycle the mezzanine board for now until I find a good price on the AS6C3216's.

- Gary

On 7/21/2015 11:48 AM, David Fry wrote:

Hi Gary,

I use the Version 03 16MB SRAM board with 2 x AS6C3216 for 8MB of RAM.

It has been built 'Stock' without modification and I've never had an issue even with the 80386 (although I confess that board is hardly in my system)

Just a thought have you double checked the address decoding jumpers ?

K3 should be position 1-2 for the AS6C3216 chips

Jumper P2 should be 1-2, and P3 should be 5-6

If these are wrong you will get address decoding issues

Regards

David

On Tuesday, July 21, 2015 at 2:35:40 PM UTC+1, Gary Kaufman wrote:

One board that's been frustrating me for a long time has been the Version 03 16mb SRAM board with the 80386 processor board 

I built one of the earlier mezzanine based boards which worked well with 2mbx8 SRAM (Cypress CY62167ELL-45ZXI 45ns 5v), but was never able to get the V3 board to work properly with 4mbx8 SRAM (Alliance AS6C3216 55ns 3.3v).  The errors were unpredictable, but most commonly resulted in 55H fill errors in the A00000-BFFFFF and E00000-FFFFFF range and almost random 1234H fill errors anywhere in memory.  The errors weren't isolated to a single bank or SRAM and wait states / clock speed didn't seem to change much, although it was more stable at very low clock speeds.

After several months of intermittently trying things, I substituted 74F240 for U9 and 74F139 for U4.  The board has run two full passes of the protected mode "J4" test without a single error.

Hopefully this might save someone else a bit of time.

- Gary

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