Xref: utzoo unix-pc.general:1880 comp.sys.att:4947 Path: utzoo!utgpu!watmath!uunet!edsews!rphroy!tkacik From: tkacik@rphroy.UUCP (Tom Tkacik) Newsgroups: unix-pc.general,comp.sys.att Subject: Re: Upgrade to 512k memory board upgrade; HwNote06.01 Keywords: memory 512k upgrade HwNote hard-ware UNIXpc 7300 Message-ID: <6072@rphroy.UUCP> Date: 14 Dec 88 20:54:12 GMT References: <441@uncle.UUCP> Reply-To: tkacik@rphroy.UUCP (Tom Tkacik) Organization: GM Research Labs, Warren, MI Lines: 45 In article <441@uncle.UUCP> jbm@uncle.UUCP (John B. Milton) writes: >I have had questions from people who couldn't quite figure out how to do the >hardare patch to the 512k memory boards, so this is as upgrade to HwNote06. >I will call this HwNote06.01. Keep the old 06 around, just append this to it. > >Once again, this concerns using the 512k (0.5M) RAM ONLY BOARD with a FULLY >populated EIA/Combo board. If you don't have both of these ingredients, you >can't make this batch of cookies. According to the manuals, there is no way to >have both a fully populated (i.e. 1.5M) Combo Card in your system AND a 512k >memory board, which would give you a complete 2M of expansion RAM. Well, as I >pointed out in HwNote06, this is not quite true, if you're willing to get out >the solding iron... > The problem is because of the way the EIA/Combo board maps the expansion memory. The 2M of expansion memory is mapped to addresses 0x200000 to 0x3fffff. The expansion bus is designed to use slot dependent addressing, with each slot at addresses: SLOT .5M Memory Board 1M Memory Board 1 0x200000-0x27ffff 0x200000-0x2fffff 2 0x280000-0x2fffff 0x200000-0x2fffff 3 0x300000-0x37ffff 0x300000-0x3fffff Which is why if two 1M memory boards are used they cannot be placed into slots 1 and 2, (or they would have the same addresses). A 1.5M or 2M memory board must use hardwired slot independent addressing. A 1.5M memory board (like the EIA/Combo baord) can have two possible address ranges 0x200000-0x37ffff, or 0x280000-0x3fffff. If it has the first, then there are no slots to put a .5M memory board, (any would have overlapping address ranges). However, if the second address range were used for the 1.5M memory board, then it could be placed in slots 2 or 3, and a .5M memory board could be placed into slot 1. The .5M board would have addresses 0x200000-0x27ffff, and the 1.5M board would have addresses 0x280000-0x3fffff. John's hardware mod would be unnecessary. AT&T must have designed it with the wrong address range! :-( (Their own S4BUS spec. documentation even describes this.) So why did they get it wrong? --- Tom Tkacik GM Research Labs, Warren MI 48090 {umix, uunet!edsews}!rphroy!megatron!tkacik