22 Feb
2010
22 Feb
'10
12:35 p.m.
On Sun, 21 Feb 2010, Chuck Guzis wrote:
On 21 Feb 2010 at 10:01, Steven Hirsch wrote:
Hm. Never realized that. However, since the pullups are generally DIP
resistor packs why not replace them with a higher value?
Why would a Shugart 801 represent a different
load than a 5.25" drive?
Aren't they both 5V TTL level interfaces?
Pullups on late 5.25" (e.g. 1.2MB) floppies as well as 3.5" drives
tend to be in the 2K range. Pullups on an 8" drive are almost always
150 ohms. How much current can that microcontroller sink for
sustained periods? You might get away with it, but I wouldn't
recommend it. Add to the
mix that 8" drive cables are usually much longer than 5.25" or 3.5"
cables (read: higher inductive load) and you have an "interesting"
cocktail. I never could make my CW MK 3 work reliably with 8" drives
until I constructed a buffer board.
Even more interesting. I've noticed that my CW MKIV+ is "fussy" about the
drives it works with. Now I have an explanation! Before going to the
trouble of building buffers, I'm more inclined to use a higher value
pullup and a shorter cable.
Steve
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