-----Original Message-----
From: cctalk-bounces at
classiccmp.org [mailto:cctalk-
bounces at
classiccmp.org] On Behalf Of Tony Duell
Sent: 04 January 2014 20:58
To: cctalk at
classiccmp.org
Subject: Re: MFM Control Signals and RD disk size
So how does it do this when the disk is yet to be formatted? In other
words, when it formats the disk how does it know what size the disk is?
Some (all?) ST412-interfaced drives report 'iilegal' head selections and
seeks
by asserting the WrtieFault/ line. The ST412 diagram
I've jsut looked at
suggests it will assert said line if either more than one head is selected
(indicating a fault i nthe selection circuitry) or if no heads are
selected
(possibly due to the head selection lines tryign to
select mroe heads than
the
drive has). There's a link on the ST412 PCB shich
is removed if the board
is
used in an ST406 (I do not mena an
ST506!) which has fewer heads, so as to cause this error if heads only
present
in the ST412 are selected
The microcotnrolelr which cotnrosl the head posiitoner stepper motor i
nthe
ST412 can also assert WriteFault/ My guess (and I do
not have the firmware
source) is that it does this if you try to step in too far.
If other drives behave in this way, its' farily easy to find out how many
cylinders and heads they have.
-tony
I can try that, wish I had a logic analyser that let me monitor what a real
disk does...
Regards
Rob