14 Jun
2005
14 Jun
'05
9:32 a.m.
From: "Randy McLaughlin" <cctalk at
randy482.com>
When replacing drives in classic systems there are some things to keep in
mind:
Newer drives are mainly compatible but not 100%.
Hi
Termination is another thing that many miss. Too much
is often just as bad as too little. Many newer drives
are not clear how to disable the termination or enable
it.
Dwight
14 Jun
14 Jun
11:04 a.m.
New subject: Replacing drives on classic systems was Wild-hair floppy drive question
From: "Dwight K. Elvey" <dwight.elvey at amd.com>
Sent: Tuesday, June 14, 2005 11:32 AM
This issue only affects 3.5" drives which no longer use the same termination
(but is compatible with).
I'll have to look up the technical details (hopefully someone will speak up
first) but basically the floppy drivers on PC's have gone from open
collector TTL to CMOS changing the characteristics of the line drivers.
I am not sure about details like maximum cable length etc. but 3.5" drives
can be mixed with TTL driven drives and termination then becomes optional.
The 3.5" drivers pull up the lines enough to make termination unnecessary,
of course you still don't want two TTL type drives terminated on the same
cable.
Randy
www.s100-manuals.com
From:
"Randy McLaughlin" <cctalk at randy482.com>
When replacing drives in classic systems there are some things to keep in
mind:
Newer drives are mainly compatible but not 100%.
Hi
Termination is another thing that many miss. Too much
is often just as bad as too little. Many newer drives
are not clear how to disable the termination or enable
it.
Dwight 
5 p.m.
New subject: Replacing drives on classic systems was Wild-hair floppy drive
This issue only affects 3.5" drives which no
longer use the same termination
(but is compatible with).
I am pretty sure I've seen some recent-ish 5.25" drives that have the
same pull-ups (not termination, strictly) as the PC-type 3.5" drives.
I'll have to look up the technical details (hopefully someone will speak up
first) but basically the floppy drivers on PC's have gone from open
collector TTL to CMOS changing the characteristics of the line drivers.
Termination is related to the cable type, and not the drivers!. You
should terminate the cable with its characteristic impedance at the far
end (from the driver), this was typically a 150 Ohm resistor. It also
acted as a pull up for the open-collector TTL drivers.
Problem was, users couldn't be relied upon to put a termination resistor
pack in the last drive on the cable. So later drives (including most 3.5"
ones) just have 1k pull up resistors on all the lines. These are not
terminators, they do not remove reflections on the cable. It seems to
work OK, but it's a kludge...
It probably is OK if you have the drives in the same box as the
controller, and thus a fairly short cable. I wouldn't want to use it on a
couple of metres of cable, though. When I put the external 3.5" drives on
my XT, I desoldered the (surface mount) resistors from the drives and
made up a terminator to plug into the end of the cable. It may have
worked without doing that, but I don't like risking my data.
-tony
7081
days inactive
7082
days old
2 comments
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