Floppy drive pin 2 question?

[Randy McLaughlin]

From: "Pete Turnbull" <pete at dunnington.u-net.com>
Sent: Monday, March 14, 2005 3:12 AM
> On Mar 13 2005, 22:45, Randy McLaughlin wrote:
>> From: "Pete Turnbull" <pete at dunnington.u-net.com>
>
>> > Michael is correct, the exact function varies from drive to drive,
> and
>> > it always involves changing the write current.  Some drives have
>> > several jumpers to affect this.
>
>> I have tried to research the issue further but can I find no
> authoritative
>> references to pin 2 being anything but an RPM select line.
>
>> If anyone has an authoritative reference stating it was not used to
> select
>> rotational speed I will be happy to change my website stating that it
> does
>> have multiple uses.
>
> [ ... ]
>
>> Please note I am not looking for what people remember it does but
> actual
>> documents from a manufacturer.  I tested it with a TEAC FD-55GFR and
> sure
>> enough it slowed the RPM when grounded.
>
> Well, how about document 5fd0050a.pdf from TEAC's website, which is the
> spec sheet for the FD-55GFR-XXXX range.  Page 1 lists the
> customer-selectable jumpers for -3xxx, -4xxx and -5xxx as including
> "LG" and "I".  Page 7 shows where all the jumpers are.  Page 8 lists
> the jumpers for -7xxx.
>
> Page 13 states (the CAPITALS are in the original document)
>
> ---------------------------- begin ---------------------------------
>
> LG strap: to select the logical meaning of the Hi/Normal DENSITY input
> signal at interface line #2
>
> LG Strap                OFF              ON
> --------------    --------------   -------------
> Density mode       HIGH     LOW     HIGH     LOW
> I/F #2 signal      HIGH     LOW     LOW      HIGH
>
> For an AT compatible system LG should be set to the off state.
>
> I Strap:
>
> Strap to select the rotational speed mode of the FDD for the Hi and Low
> density modes.
>
> ---------------------------- end ---------------------------------
>
> In other words, Pin 2 is the Density Select signal, and can be jumpered
> to work so that 0V (signal active) sets HD and inactive sets low
> density (SD/DD, or FM/MFM).  Normally it's not fitted, so active (low)
> sets low density and inactive (or open-circuit) sets high density -- as
> you woould want for an IBM AT or similar.
>
> The "I" jumper controls whether the Density Select signal *also*
> controls the speed -- a *secondary* function of the Density Select.  If
> fitted, speed changes when density does; if not fitted, speed is fixed
> at 360 RPM.
>
> Pages 16-21 of the same PDF file on TEAC's website are a scanned copy
> of TEAC's "FD-55-GRF-XXXX Instalation Guide" for use with IBM AT, which
> clearly shows the factory settings of the jumpers, with neither "LG"
> nor "I" fitted, so Pin 2 selects density as usual, and the signal on
> pin 2 does not affect the speed, which is fixed at 360 rpm.
>
> If you want more, I have data for Mitsubishi MF504C-310MP, on which
> jumper SS sets single speed (360 rpm) without affecting density
> selection, same for Mitsubishi M4854-35, Panasonic JU-475-2.AGG (jumper
> AX makes density select on pin 2 be latched when drive is selected,
> BX/CX/JX determine if speed is determined by density select or is
> fixed, and 1M forces it to ignore the density select signal on pin 2),
> and Fuji FDD5883AOK (Toshiba) which has a jumper from pin 2 to ground
> labelled "DD" for double density and described as disabling HD (jumpers
> DE/DX are described as to set the speed according to the density, or
> fixed).
>
> Think about this:  All HD-capable 5.25" drives need a way to set the
> density (by changing the write current) for either 300 oersted media or
> 600 oersted media.  The drive has no way to tell on its own.  Therefore
> there must be some signal defined to do this.  AT controllers can write
> both densities at 360 rpm (they just use a 300kbps clock instead of a
> 250kbps clock), so they don't actually need to change the speed.
> Therefore the signal previously unused (or, rarely, used in
> non-standard vendor-dependant ways) on pin 2 is the density signal;
> using it to reduce the speed is an optional extra.
>
> Your FD55 happens to have a jumper fitted to make the speed change when
> you change the density, that's all.
>
> -- 
> Pete Peter Turnbull
> Network Manager
> University of York


You have mis-read the table.

Pin 2 can only change the speed to 300 RPM by lowering pin 2, with pin 2 
high no matter what the drive runs at 360 RPM.

The density mode can be high with pin 2 high or low with pin 2 high 
depending on jumpering.

The one and only standard the document gives for pin 2 is speed change.

All of the original AT controllers required two speed drives.  Later 
controllers added the 300K transfers.


Randy
www.s100-manuals.com


Randy
www.s100-manuals.com