FC5025 USB 5.25 floppy controller - first report

23 Feb 2010

...
   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?  
 Hm.  Never realized that.  However, since the pullups are generally DIP 
 resistor packs why not replace them with a higher value? 
Well, you could, but I wouldn't. The resistors are not only pull-ups, 
they also terminate the cable (regarded as a transmission line). I am a 
great beleiveer in properly terminated cables, reflections on said cables 
cause all sorts of 'interesting' problems.

I suspect it would work with 1k pull-ups and a short cable, but 
constructing a buffer board is not going to take long (it's only 2 or 3 
14 pin TTL chips), and it means it _will_ work. If you have problems with 
data corruption, etc, you then know it's not due to ringing on the cable.

-tony

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FC5025 USB 5.25 floppy controller - first report