View Full Version : IBM Enhanced Memory Expansion Adapter manual?

March 30th, 2017, 11:02 AM
Does anyone have a copy or scan of the Guide to Operations for the Enhanced Memory Expansion Adapter, 74X7715 shown in the image below?

I picked up an IBM AT which contained two EMEA boards, one ASM 55X3543, the other ASM 30F5368. They look identical and both work with pairs of 1MB SIMMs. The AT has a Type 1 motherboard with piggybacked DRAM chips. Three of the chips appear to be bad so I removed the second bank and changed the J18 (http://minuszerodegrees.net/5170/misc/5170_motherboard_switch_settings.htm) jumper and only have 256KB installed now.

I have been unable to correctly configure either EMEA board to fill base memory from 256KB though 640KB plus provide extended memory starting at 1MB.

According to this link (http://stason.org/TULARC/pc/io-cards/I-L/IBM-CORPORATION-Multi-I-O-card-ENHANCED-MEMORY-EXP.html) switches 6 and 7 should be set to indicate that there is 256KB of base memory and switches 1 through 5 should be set to indicate that the extended memory should start at 1MB. That sort of seems to work initially if I use the setup program to say there is 640KB of base memory and 1664KB of extended memory (2048KB on the EMEA minus the 384KB to fill base memory to 640KB). Then at power on the POST will count up to 2304KB (256KB on motherboard plus 2048KB on EMEA) but then it reports 040000 0700 203-Memory Address Error and only 256KB.

I took a quick look at the BIOS memory testing code and it wasn't extremely obvious at first glance exactly what might be causing that error. IBM 5170 - Technical Reference - 6280070 - SEP85 (http://minuszerodegrees.net/manuals/IBM_5170_Technical_Reference_6280070_SEP85.pdf) TEST 2, page 5-65

I tried adding an Intel Above Board configured to fill base memory between 256KB and 640KB and configured the EMEA to only supply extended memory starting at 1MB and that worked. I also swapped in a Type 2 motherboard with 512KB and configured the EMEA to fill base memory from 512KB through 640KB and supply the rest as extended memory starting at 1MB and that also worked.

So I have some workarounds, use the Type 2 motherboard with 512KB with the EMEA, use the Type 1 motherboard with only 256KB with the Intel Above Board and with or without the EMEA, maybe acquire some replacement piggyback DRAM chips to get the Type 1 motherboard back to 512KB and try that with the EMEA. But still it would be nice to figure out how to get the 256KB Type 1 motherboard to work with just the EMEA to fill base memory plus extended memory.

Also, this link (http://stason.org/TULARC/pc/io-cards/I-L/IBM-CORPORATION-Multi-I-O-card-ENHANCED-MEMORY-EXP.html) shows 7 pairs of SIMM sockets when the board actually has 6 pairs, so I wonder if there are other errors on the page which are correct in the actual manual.