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000121_news@newsmaster….columbia.edu _Thu Oct 16 16:47:54 1997.msg
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Newsgroups: alt.sys.pdp11,vmsnet.pdp-11,comp.protocols.kermit.misc
Subject: Re: DX11 baud rates under RT11
References: <RJM.97Oct15164024@swift.eng.ox.ac.uk> <6232gg$jnu$1@nntp.ucs.ubc.ca> <RJM.97Oct15235003@europa.ox.ac.uk> <tsw-1610971108160001@cypher.cagent.com>
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From: wilson@dbit.com (John Wilson)
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In article <tsw-1610971108160001@cypher.cagent.com>,
Tom Watson <tsw@cagent.com> wrote:
>Others have posted some commercial solutions to the "problem" but it
>really isn't that bad. The basic 8" floppy uses the same data rates as a
>1.2Meg 5 1/4" floppy. The big problem is the connector. The 8" drive
>uses a 50 pin connector, and the 5 1/4" drive uses a 34 pin connector.
>All of the signals are there, but as usual, IBM long ago diddled with
>things a bit.
FYI this isn't quite 100% true, the 34-pin interface is missing TG43
and the 2SIDE pin and I think there's a READY pin. Also the 8" disk
uses a head load pin but not a motor-on pin (the 8" motor runs all the
time). You can get around most of these, and you don't need TG43 for
reading (some drives keep track of the current track themselves and
don't need TG43 at all), but for writing I imagine you could get into
trouble if you don't reduce the write current on inner tracks using
this pin. Some PC FDCs (like the 37C65) generate the TG43 (a.k.a. /RWC)
pin but only under certain circumstances (the 37C65 has 3 different modes,
I think this pin is used for /RPM in AT-compatible mode), the CompatiCard
IV has a software-programmable output for setting it (which PUTR does),
and I guess you could use a LPT port pin with an OC driver to do it from
software. The PC doesn't have a use for the 2SIDE or READY pins though
so those don't matter.
John Wilson
D Bit