Building new S100 floppy system - test-drb@ccmp.vtda.org

21 May 2006

AFAICG the 1770 is a double sided controller chip,
being that its used in the RE Robot brain-board.
Purchance is it pin compatible with the dopier LOL
1771?
--- cctech-bounces at classiccmp.org
<ard at p850ug1.demon.co.uk> wrote:
...
  > 
 > All:
 > 
 >  
 > 
 >             I have several random parts I'm going to pull together to
build
...
  > a "new" floppy system for my IMSAI. I
have an SD Sales Versafloppy
...
  > controller card (which used the FD1771B
controller) and several 5.25" floppy
...
  > drives (all soft sectored). The Versafloppy
manual indicates that it will
...
  > work with a Shugart SA400/450. When I look up the
specs on the SA400, it
...
  > indicates that the unformatted capacity is 109.6k
and the formatted capacity
...
  > is 81k. I didn't read the entire manual but
this look like SSSD specs.
...

 The 1771 is a single density (FM) controller only. 

 >             I of course don't have any floppy drives like this but I have
...
  > several original PC drives (TM-100 and others)
and several 360k drives of
...
  > various types.
 > 
 >             The question is this: can I use these later drives on this
...
  > controller without problems? If there are
problems, what might they be?
...

 It's almost impossible to make a drive that will handle double density 
...
  but not single density. So your '360K' drives
will be fine in that 
...
  respect. 

 There are likely to be 2 other differences  : 

 1) The SA400 was, IIRC, a single-sided unit. Your 360K drives are double 
...
  sided. The controller may well not support
double-sided operation, and it 
...
  may use the side select pin for something else (DS3
was one common use I 
...
  think). You may need to do a little bit of
modification in this area.
...

 2) I think the SA400 was a 35 cylinder drive, '360K' drives are 40 
...
  cylinder. This shouldn't matter unless, for some
unknown reason, the 
...
  controller only sends 35 step pulses when it tries
to restore to cylinder 
...
  0. AFAIK any standard use of the 1771 won't
suffer
from this. 

 -tony 

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