Cromemco 4FDC, How do you format a disk?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Jul 27 20:36:14 1999

Some 8" drives, notably those from Shugart, had optional circuitry which you
could install yourself, BTW, to do things like recover clock from the data
stream, hence the SEPDAT and SEPCLK signals, and mask the sector pulses if
you wanted to use hard sectored media in a soft-sectored mode, or whatever.
The signal you are probably going to want is the raw data, which is common
to all of the various versions. Oddly enough, the half dozen or so SIEMENS
drives I have all have this logic as standard.

the use of the same signal as both clock and data stems from the fact that
FM data has the clock embedded in it. Hence, if you don't separate them on
the drive, the controller does that by taking the signals whether they're
separated or not, and feeding them to the respective circuits whose job it
is to process them. They then use the signals either combined or separated,
and process them as they need.

These circuits are the things which got many people into the habit of
referring to a drive as being either single or double density capable.
Without them, they're all capable of either, since the rate at which flux
reversals are written on the medium is still the same. MFM simply
integrates the clock and data in a way which doesn't waste half the
bandwidth on clock pulses.

Dick


-----Original Message-----
From: Bill Sudbrink <bill_at_chipware.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Tuesday, July 27, 1999 4:53 PM
Subject: RE: Cromemco 4FDC, How do you format a disk?


<snip>
>
>According to the docs, you have to tell the controller
>which drive type it is talking to (bit 4 at I/O address
>34 hex). Looking at the schematics, it sure looks like
>it blindly shoots signals to both connectors. FDAT is
>connected to pin 30 on the 34 pin header and pin 48 on
>the 50 pin header. Hmmm... what's going on here? Pin 48
>is SEP DATA, used with hard sectored drives isn't it?
>Pin 50 is connected to FCLK as well.
>
>What gives?
Received on Tue Jul 27 1999 - 20:36:14 BST