Floppy Diskdrive pinout

connector or cable wiring scheme

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34 pin
IDC male connector
at the motherboard & diskdrives

Controller pinout:

Pin

Name

Dir

Description

2

/REDWC

Density Select

4

n/c

Reserved

6

n/c

Reserved

8

/INDEX

Index

10

/MOTEA

Motor Enable A

12

/DRVSB

Drive Sel B

14

/DRVSA

Drive Sel A

16

/MOTEB

Motor Enable B

18

/DIR

Direction

20

/STEP

Step

22

/WDATE

Write Data

24

/WGATE

Floppy Write Enable

26

/TRK00

Track 0

28

/WPT

Write Protect

30

/RDATA

Read Data

32

/SIDE1

Head Select

34

/DSKCHG

Disk Change

Floppy Diskdrive pinout (Shugart interface):

Pin

Name

Dir

Description

2

/DCD

Disk Change Detect

3

Key

no pin in this position

4

/DS3

Device Select 3. Not sure but Amiga 500"s schematics reveal that
this signal might be used for motor control of internal DF1: on the
Amiga 2000

6

/INUSE

A common open-collector LED driver signal? I have never seen
this signal used anywhere.

8

/INDEX

Index

10

/DS0

Device Select 0

12

/DS1

Drive Sel B

14

/DS2

Device Select 2

16

/MTRON

Motor On

18

/DIR

Direction

20

/STEP

Step

22

/WDATE

Write Data

24

/WGATE

Floppy Write Enable

26

/TRK00

Track 0

28

/WPT

Write Protect

30

/RDATA

Read Data

32

/SIDE1

Head Select

34

/RDY

Drive Ready

On a standard floppy drive there is absolutely no way to remap the
motor on signal to another pin with jumpers. Therefore to have independent
motor control for two drives the cable must provide this remapping with
the traditional seven-conductor twist. If you jumper a floppy drive to
work as drive A (unit 0) and connect it to an "IBM PC" controller with a
direct cable, the drive will be selected when the controller tries to turn
on the motor of drive A but nothing will happen and the drive"s motor will
rotate when drive B"s motor is turned on.

The original Shugart interface (from which the "IBM PC" floppy
interface is derived a long time ago) doesn"t have separate motor on
signals for the floppy drives but it does have a total of four device
select lines. I have also seen floppy drives that won"t turn on their
motors unless the according device select signal is driven low. My guess
is that this kind of drives strictly follow the original Shugart
standard.

Also many synthesizers that have floppy drives use the standard Shugart
interface pinout. This is why after replacing a faulty drive many people
ask around the Internet why their new floppy drive doesn"t work when
connected to the synth but works fine on their PC.

The same thing affects the classic Amiga. It uses a very slightly
modified Shugart interface pinout at the motherboard (the other /MTRON on
pin 4) and a "PC" drive just doesn"t work correctly unless the /DCD is
remapped to its original pin. The correctly mapped /DCD is enough for
AmigaOS but many trackloaders (X-Copy Pro for example) require the /RDY
signal which the drive should set low when the motor rotation has
stabilised. This signal does exist on most drives but at worst it requires
relocating a soldered SMD jumper on the circuit board.

The floppy cable has 34 wires. There are normally five connectors on
the floppy interface cable, although sometimes there are only three. These
are grouped into three "sets"; a single connector plus two pairs of two
each (for a standard, five-connector cable) or three single connectors.
This how the connectors are used:

Controller Connector: The single
connector on one end of the cable is meant to connect to the floppy
disk controller, either on a controller card or the
motherboard.

Drive A Connectors: The pair of
connectors (or single connector in the case of a three-connector
cable) at the opposite end of the cable is intended for the A:
floppy drive. This is explained in more detail below.

Drive B Connectors: The pair of
connectors (or single connector in the case of a three-connector
cable) in the middle of the cable is intended for the B: floppy
drive.

The reason that the standard cable uses pairs of connectors for
the drives is for compatibility with different types of drives. 3.5"
drives generally use a pin header connector, while 5.25" drives use a card
edge connector. Therefore, each position, A and B, has two connectors so
that the correct one is available for whatever type of floppy drive being
used. Only one of the two connectors in the pair should be used (they"re
too close together to use both in most cases anyway). The more common pin
header (IDC) connector is shown below.

The three-connector cables are found either in very old systems or in
ones where the manufacturer was trying to save a few pennies. They reduce
the flexibility of the setup; fortunately these cables can be replaced
directly by the five-connector type if necessary.

You will also notice that there is an odd "twist" in the floppy cable,
located between the two pairs of connectors intended for the floppy
drives. Despite the fact that this appears to be a "hack" (well, it really
is a hack), this is in fact the correct construction of a standard
floppy interface cable. There are some cables that do not have the twist,
and it is these that are actually non-standard! What the twist does
it to change the connection of the drive on the far end of the twist so
that it is different than the drive before the twist. This is done to
cause the drive at the end of the cable to appear as A: to the system and
the one in the middle to be as B:.

Here"s how it works in detail. Traditionally, floppy drives used a
drive select (DS) jumper to configure the drive as either A: or B: in the
system. Then, special signals were used on the floppy interface to tell
the two drives in the system which one the controller was trying to talk
to at any given time. The wires that are cross-connected via the twist are
signals 10 to 16 (seven wires). Of these, 11, 13, and 15 are grounds and
carry no signal, so there are really four signals that are inverted by the
twist. The four signals that are inverted are exactly the ones that
control drive selection on the interface. Here is what happens when the
twisted cable is used:

Line 10

Line 12

Line 14

Line 16

Controller Signals

Motor Enable A

Drive Select B

Drive Select A

Motor Enable B

Drive Before the Twist Sees

Motor Enable A

Drive Select B

Drive Select A

Motor Enable B

Drive After the Twist Sees

Motor Enable B

Drive Select A

Drive Select B

Motor Enable A

Since the signals are inverted, the drive after the twist responds to
commands backwards from the way it should; if it has its drive select
jumpers set so that it is an A: device, it responds to B: commands, and
vice-versa.

One might ask why the twist was needed. In short, because it was a big
time-saver during setup back in the days when it was quite common to find
two floppy drives in a machine. Without the twist, for two floppy drives
to be used, one had to be jumpered as A: and the other as B:. With the
twist, it was possible to leave them both jumpered as B:, and whichever
was after the twist will appear to the system as A: because the control
lines are inverted. Changing which drive is A: and which is B: is as easy
as switching the cable. In systems with only one floppy drive, only the
connector after the cable should be used. Large manufacturers, therefore,
could arrange to have all of their floppy disks configured the same way
without having to pull jumpers as the PC was assembled.

In order for this system to work, both drives must be jumpered as B:
drives. Since the floppy cable with the twist is standard, this jumpering
scheme has become the standard as well. Virtually all floppy disks that
you purchase come pre-jumpered as B: drives so that they will work with
this setup.

If this whole idea sounds similar to the seldom-used cable select
protocol for IDE/ATA hard disks, that"s because it is essentially the same
thing. IDE/ATA hard disks require you to change the master/slave jumpers
in a similar manner, and cable select was invented to do away with this.
The difference is, as usual, just one of inertia and history; the floppy
drive system is the standard while cable select never caught on for hard
disks.

Some newer BIOSes have taken things a step further. They include a BIOS
parameter that will invert the A: and B: signals within the controller
itself. When enabled, this lets you reverse whichever drive is A: with the
one that is B:, without requiring you to even open the case. Note however
that this is not compatible with all operating systems: in particular,
both Windows NT and Linux can malfunction with this swap feature set,
which can cause serious problems when trying to install the operating
system. The reason this happens is that the swap setting only affects the
way the BIOS handles the floppy drive, and confuses operating systems that
go directly to the hardware.

Apparently, there is yet another floppy cable variant out there, that
is used by some manufacturers. In this setup, there are actually two
twists in the floppy cable. The drive placed after the first twist, in the
middle of the cable, is A:, much as it is with the standard one-twist
cable. The drive placed after the second twist is B:. The second twist
"reverses" the effect of the first one and makes the connector at the end
of the cable operate the same way a drive that appears before the twist in
a regular cable does.

On some mainboards pin 3 is used as the key (missing pin) and on some
pin 5 is used as the key pin, while a lot of mainboards don"t have the key
pin removed at all. This can all cause problems when using cables which
have the key pin hole closed. As all odd pins are ground there are no
technical implications in modifying such cables by removing the key pin
closure by force.

Note: Direction is Computer relative Diskdrive.
Note:
All odd pins are GND, Ground.
Note: Can be an Edge-connector on old
PC´s.

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34
pin IDC female connector
at the cable

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Pinouts.ru > Disk drives connectors pinouts
listing > Pinout of Floppy Diskdrive and layout of 34 pin
IDC male connector and 34 pin IDC female connector

Information:

should be correct

Source(s) of this and additional information: www.citizen.co.uk/fdd/ (including
some pinouts like 26-pin floppy connector used on laptops and other
interfacing information) and others

Contributor: archyx and others, Sven Olaf
Kamphuis

7 reports

Last updated at 2008-07-27 20:59:31.
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