23 Feb
2010
23 Feb
'10
11:13 p.m.
On Tue, 23 Feb 2010, Tony Duell wrote:
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.
Fair enough :-). The TTL chips of which you speak are bidi bus
transceivers, correct? Would you use the R/W line to switch directions,
or is there other magic involved?
Any construction tips? (Schematic would be nice - but hand-waving works,
too!)
Steve
--
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?