From: Adam Quantrill (aquantrill_at_scigen.co.uk)
Date: Wed Apr 07 1999 - 07:02:38 EDT
I got the data sheets on the chips and my assumption was correct - each is 512k*9bits. I have lifted the power supply pins on a number of the chips and got '1668KB OK' so I then added the expansion ram and that quite happily sits on top of the new memory boundary. I'm not sure that I have disconnected the chip that was giving gyp (!) but it now all works albeit with slightly reduced memory.
The question still stands, however, what is the arrangement of memory chips in the memory map? I reckon on there being 16 bit words so I have to disconnect maximum 2 chips, leaving me with 3MB on the motherboard. However if the bus were 32 bits wide I'd have to disconnect 4 chips. But the question is which 2/which 4? I've disconnected a few chips at a time but there doesn't seem to be an unambiguous logical relationship (so far) between which chip/what memory you get.
Anyone with any clues as to the placing of the memory chips on this motherboard?
- Adam
______________________________ Reply Separator _________________________________
Subject: [755C] Memory parity problem on motherboard
Author: MIME:Adam Quantrill <aquantrill_at_scigen.co.uk> at INTERNET
Date: 30/03/99 09:54
I've disassembled my 755C and there are no obvious cracks or bad soldering on what I take to be the RAM chips (HM514900ALTT7R) but nevertheless I intend to reflow them just in case. Does anyone know the correspondence of memory location to chip? As there are 8 of them I assume it's one chip per half megabyte, each being 9 bits wide as you can have parity. I'd rather reflow and/or replace just the duff chip, and as the error is at 3.7MB it will be the last one.
Any advice in this area would be appreciated.
- Adam
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Scientific Generics Limited Tel: +44 1223 875200
Harston Mill Fax: +44 1223 875201
United Kingdom http://www.generics.co.uk
Harston
Cambridge
CB2 5NH
Registered in England No 2081960
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