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From: torvalds@cc.helsinki.fi
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: TECHNICAL ?'s ABOUT 1.44M FLOPPIES
Message-ID: <1991Feb17.152818.4901@cc.helsinki.fi>
Date: 17 Feb 91 15:28:18 GMT
References: <1991Feb12.215709.17456@coplex.uucp> <355@einstein.eds.com>
Organization: University of Helsinki
Lines: 48

> In article <1991Feb12.215709.17456@coplex.uucp>, dannie@coplex.uucp (Dannie Gregoire) writes:
>> I have been trying to find some information on the hardware differences
>> between 720K and 1.44M floppies.  Specifically, what are the differences
>> in the pin outs (and signals sent to the PC) between the drive's connectors.
>> 
>> What signal (if any) is sent to the PC when the drive detects that a high
>> densisty has been inserted.

Right, this info is straight from the EPSON SMD-340 3.5" floppy drive
manual (not guaranteed, but should of course work for others as well :-)

Pin	Name	what?

2	HDI	High density in (low in 2MB mode (2MB unformatted=1.44MB))
4	NC
6	DS3	Drive select 3 (low -> selected)
8	IDX*	Index
10	DS0	Drive select 0
12	DS1	Drive select 1
14	DS2	Drive select 2
16	MON	Motor on (low - on)
18	DRTN	Direction (low - step inwards)
20	STP	step (transition low->high steps motor, usuallu 3 ms)
22	WTD	Write data
24	WTG	Write gate (active low)
26	TK00*	Track 0 (low means we are on track 0)
28	WPT*	Write protect (low means write protected)
30	RDD*	Read data
32	SSL	Side select (note low means side 1, high means side 0)
34	DCH*	Disk change

pins 1,3,5 not connected, others grounded.
* means signal from disk drive, otherwise to drive unit.

NOTE! The HDI is not from drive to computer but the other way around.
This can force the drive to use 2MB mode (1.44MB). This is in fact not
used on most drives to my knowledge, as the drive senses the density
from the disk covering. This can be enabled by a jumper on my drives.

There are drives available that use pin 2 as HDO (High density out) to
let the computer sense the density used, but I wouldn't know where to
find them. Some can also use pin 34 to indicate RDY, ie that the drive
is up to speed etc. The MON can also be ignored by some drives which use
the select lines to activate the motor as well.

This information is in no way guaranteed to be correct.

		Linus Torvalds  torvalds@cc.helsinki.fi