8" drive support on PC's

[Randy McLaughlin]

From: "Pete Turnbull" <pete at dunnington.u-net.com>
Sent: Thursday, March 17, 2005 5:09 PM
<snip>
> Well, I looked at the data sheet for the WD37C65, which used to be
> fairly common, and the answer is "sort of".  Pin 39 is the one that
> you'd be interested in.  It's an output labelled "/RWC,/RPM" and when
> it's low, and the controller is in Base Mode, it says it causes a
> reduced write current when bit density is increased towards the inner
> tracks, being active when track > 28 (I think that refers to 40-track
> drives, which would be 56 on an 80-track drive).  This is very similar
> to to the TG43 signal, except for being relative to a different track,
> but it's not on the same pin as /DIRECTION (Pin 31).  I can't help
> wondering if "28" is a misprint for "23" or something like that, but I
> checked two separate printings of the data sheet and both said "28".
>
> It also says this function changes when in AT/EISA mode (it then
> becomes completely under program control, and appears to be intended to
> be used to set the density and/or speed for the whole disk) :-(
>
> However, if you have control over the FDC rather than letting the BIOS
> or DOS do it for you, you could make it do what you wanted.
>
> I also looked at the Intel 82078 FDC, which is a successor to the 8272,
> in either a 64-pin QFP package or a 44-pin PLCC, either 5V or 3.3V,.
> and it was an antecedent of many of the multi-I/O chips.  Unfortunately
> it doesn't give enough detail.
>
> Lastly, I looked at the NatSemi DP8473.  It has /DIRECTION on pin 4
> (PLCC version), and /LC (low current) on pin 51.  Pin 51 just goes high
> for HD media and low for SD/DD media (actually it goes low when 250kbps
> or 300kbps data rates are set, instead of 500kbps).  So it doesn't look
> like that does what you'd want, either.
>
> -- 
> Pete Peter Turnbull
> Network Manager
> University of York

Yes I agree with what you said but it misses the point:

Today density select is a general purpose IO pin, originally the 765 used 
the direction pin as a dual purpose pin.

This dual purpose description is now gone but maybe not the action.

There is no need for TG43 in todays PC's, at least not as far as the 
manufacturers are concerned.  When the need for a "new" density select line 
came it was accomplished through a separate IO but was the old reduced 
current logic removed?


Randy
www.s100-manuals.com