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
