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- Path: sparky!uunet!sun-barr!cs.utexas.edu!wupost!waikato.ac.nz!comp.vuw.ac.nz!actrix!David.Empson
- Newsgroups: comp.sys.apple2
- Subject: Re: Question about the smartport...
- Message-ID: <1992Jul24.141016.3843@actrix.gen.nz>
- From: David.Empson@bbs.actrix.gen.nz
- Date: Fri, 24 Jul 1992 14:10:16 GMT
- Sender: David.Empson@actrix.gen.nz (David Empson)
- References: <1992Jul18.184515.1985@news.columbia.edu> <1992Jul24.033112.8121@vela.acs.oakland.edu>
- Organization: Actrix Information Exchange
- Lines: 39
-
- In article <1992Jul24.033112.8121@vela.acs.oakland.edu> mkheintz@vela.acs.oakland.edu (Michael Heintz) writes:
- >
- > Somewhere in our GS reference book(s), I was able to verify that you can
- > chain up to four 3.5 drives to the smartport. However, recent research
- > shows the following results:
- > 2 - 3.5 Drives (max)
- > 2 - 5.25 Drives (max)
- > 4 - UniDisk Drives (max)
- > Maximum # of devices = 4.
- >
- > However, there may be a chance that additional 3.5 drives (besides the
- > UniDisk) can be chained and recognized by ProDOS 8, it may be a limitation
- > of the GS/OS Appledisk3.5 drivers.
-
- Nope. The Smartport bus can only address two Apple 3.5" drives. There
- are only two "select" lines.
- If you tried to plug in more than two, you'd probably find one of the
- following situations:
-
- (a) Drives 3 onward wouldn't do anything.
- (b) Drives 3 onward all operate in parallel with drive 2.
- (c) All odd numbered drives operate in parallel, as do all even number drives.
-
- Either case (b) or (c) would probably damage the IWM chip in the
- drives, so don't try plugging in more than two Apple 3.5" drives unless
- you want to destroy them.
-
- Similar problems occur with 5.25" drives - you can only have two of
- them per slot.
-
- The UniDisk 3.5 is handled differently: it has a microprocessor inside
- it, and uses an address byte rather than a select line. There are 7
- bits in the address byte, allowing up to 127 UniDisk 3.5" drives in
- theory. Power supply and signal strength problems limit it to 4 drives.
- --
- David Empson
-
- Internet: David.Empson@bbs.actrix.gen.nz EMPSON_D@kosmos.wcc.govt.nz
- Snail mail: P.O. Box 27-103, Wellington, New Zealand
-