Hi!

I have been mostly lurking here, but I have been designing a DRAM board for the 
HP1000 A-Series, using a more
modern 72-pin SIMM. The A400 can adress 32Mb of parity ram so I use 17 bits on 
a 64Mb SIMM. I have taken
inspiration from the original HP12103X boards and tried to keep away from 
esoteric parts. The board prototype
works now and passes all tests, except that it gives a partity error in one of 
the first addresses (ie 2,7,10
octal) when booted cold. If I then run a %T it works fine, and also if I reset 
by bringing PON low.

I have tested with different SIMMs and the two different types I have tested 
both exhibit the same issue. The
64Mb one has Samsung KM41C16000C chips.

As this is for hobby-use, it is not a big deal as the board works, otherwise, 
but it is annoying.

If anyone here, and I expect there are several that have worked with DRAM 
chips, have any suggestions on this
issue or the board in general?

Schematic is 
here:www.dalton.ax/hp1000/Memory/HP1000RAM_SIMM_Buffers_20241130.pdf

Yes. I have also written protocol decodes for the KingstWiz LA5032 32-bit LA to 
analyse the HP memory bus if
anyone is interested.




-- 
Med vänlig hälsning

Anders Gustafsson, ingenjör


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