Floppy Disk Drive Interface

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Floppy Disk Drive Interface

Postby 1024MAK » Thu Apr 29, 2010 10:35 pm

I list here some general information on the Floppy Disk Drive Interface (Shugart floppy disk drive interface) for 5¼", 3½", 3" drives.

Note that more than one variant of the 34 way interface has been used over the years. Atari used one version and the IBM PC range and clones used a slightly different variant. Other computer and equipment manufacturers used other variations.
So a lot of the information here is not Atari specific.

When I modified my Atari 520 STFM many years ago bought and tried a number of different 3.5" drives. I never had a problem with the Atari not seeing any of these drives (many different makes and models). Of the data sheets that I got my hands on back then, each disk drive manufacturer had a slightly different set of signals for the 34 way connector! These data sheets are paper versions.

Note that the Atari floppy interface is not completely to the Shugart floppy disk drive interface standard. The floppy drive interface was in use long before the IBM PC computers came along. For some reason IBM used a different method and that method is now the current (and most likely the last) "standard".

But then it looks like the floppy interface suffered from the same problems as the serial "RS232", parallel printer (Centronics) and SCSI/ASCI interfaces (to name but a few) where each equipment manufacturer used a sub-set of the known "standard" and used the signals to suit their own application. And of course as time moves forward tweaks are made to the "standard" interfaces on new equipment so they are now different to the original "standard"! :lol:

http://jimwarholic.com/2008/12/the-flop ... design.php

http://groups.google.ms/group/sci.elect ... fcd31d61a#

http://pinouts.ru/Storage/InternalDisk_pinout.shtml

http://www.walshcomptech.com/ohlandl/fl ... pin_Header

http://www.walshcomptech.com/ohlandl/fl ... nouts.html

http://www.interfacebus.com/PC_Floppy_Drive_PinOut.html

http://www.vintage-computer.com/vcforum ... -connector

http://www.computerhope.com/jargon/f/flopcabl.htm

http://jimwarholic.com/2009/04/fdd-flop ... lators.php

Drive manufacturer data sheets:-
http://www.techtravels.org/amiga/SAMSUN ... 070103.pdf
http://www.citizen.co.uk/fdd/index.htm (has links to pages with a couple of PDF files)
TEAC:
datasheet.pdf


http://sony.storagesupport.com/product/192#documents

Other floppy info:- http://matthieu.benoit.free.fr/102.htm

Floppy IC (chip) controller manufacturer data sheets / information:-
http://en.wikipedia.org/wiki/Western_Digital_FD1771

If anyone wishes to add to this, please do.
Also if anyone would like me to scan in and upload images of the paper data sheets let me know. :)
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Last edited by 1024MAK on Mon Aug 16, 2010 10:40 pm, edited 1 time in total.
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Re: Floppy Disk Drive Interface

Postby 1024MAK » Wed May 19, 2010 1:06 am

Some more information and pictures

Floppy drive power connector (red wire is +5V supply, yellow wire is +12V supply and both the black wires are ground (0V):
Floppy drive power connector.jpg


Floppy drive power connector on Panasonic JU-363 drive:
Floppy drive power connector on Panasonic JU-363 drive.jpg


Floppy drive power connector on Sony MPF920 drive:
Floppy drive power connector on Sony MPF920 drive.jpg


Floppy drive signal connector on Panasonic JU-363 drive:
Floppy drive signal connector on Panasonic JU-363 drive.jpg


Floppy drive signal connector on Sony MPF920 drive:
Floppy drive signal connector on Sony MPF920 drive.jpg


A typical Physical Interface & DC Power Profile of a DS DD drive:-
Physical Interface & DC Power Profile .jpg
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Re: Floppy Disk Drive Interface

Postby 1024MAK » Wed May 19, 2010 2:14 am

Image of the Atari ST Owner's Manual - Floppy Disk connections (14 pin DIN):
's Manual - Floppy Disk connections (14 pin DIN) .jpg
Note that this is the view looking into the connector on the Atari, or looking at the solder pins on the inside (cable connection point) of the 14 way DIN plug.

Atari floppy signal connection info - how to connect a "standard" Double Sided Double Density (DS DD) drive with a 34 way connector to the Atari ST 14 way DIN connector:
Atari floppy signal connection info 33%.jpg
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Re: Floppy Disk Drive Interface

Postby 1024MAK » Thu Jul 29, 2010 3:21 pm

Atari External Floppy Disk Drive Adapter

Code: Select all

        Atari External Floppy Disk Drive Adapter

  ATARI       34 way IDC   Signal Name and Function
  STFM       connector for
14 pin DIN    Disk Drive
   N/U            1        Not used on Atari
   N/U *1 <----   2        Density Select
   N/U    ---->   4        In Use (tells drive to light it's LED)
   N/U    ---->   6        Drive Select 3 (DS3) - Not used on Atari
    4     <----   8        Index
    5     ---->  10        Drive Select 0 (DS0)
    6     ---->  12        Drive Select 1 (DS1)
   N/U    ---->  14        Drive Select 2 (DS2) - Not used on Atari
    8     ---->  16        Motor On
    9     ---->  18        Direction Select
   10     ---->  20        Step
   11     ---->  22        Write Data
   12     ---->  24        Write Gate
   13     <----  26        Track 00
   14     <----  28        Write Protect
    1     <----  30        Read Data
    2     ---->  32        Side Select
   N/U    <----  34        Ready / Disk Change - Not used on Atari
    3            *2        Ground (GND / 0V)
    7            *3        Ground (GND / 0V) / Density Select (see notes)

Notes
*1     Density Select is not normally used on Double Density (DD) drives.
       On some High Density drives this is an output from the drive to signal that a HD disk is in the drive.
*2     Connect pin 3 on the Atari 14 way DIN to the odd numbered pins 3 to 33 on the IDC drive connector,
       which are all Ground (GND / 0V) connections.
*3     On modified Atari's pin 7 of the 14 pin DIN is disconnected from ground and used for the Density Select
       signal from pin 2 of the IDC drive connector. On unmodified Atari's this is another Ground (GND / 0V)
       connection.

This is my 14 way DIN to 34 way IDC floppy adapter that I made up many years ago. I have not yet modified it to made it HD compatible, but will do in due course.
Note that the IDC connector "socket" on the cable at the stripboard end has the cable connected "upside down" compared to a standard "IBM PC" drive lead, so if you wish to copy this design, you will need to make up your own IDC ribbon cable drive lead (or modify a PC one). The red stripe indicates the core used for pin 1, but because the connections are reversed on the PCB connector, on the IDC cable "socket" the blue stripe is connected to what is supposed to be pin 1 on the IDC connector. I hope I have not confused the issue too much :lol:
So for example, the yellow wire (the one on the end, not the middle one) going to the 14 way DIN plug is "Side Select" and is connected to pin 2 on the 14 way DIN plug. The next wire, the white one is "Read Data", the next, (orange) wire is "Write Protect" etc...
My DIN to IDC floppy adaptor.jpg
My DIN to IDC floppy adaptor #2.jpg
My DIN to IDC floppy adaptor #3.jpg
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Re: Floppy Disk Drive Interface

Postby 1024MAK » Sat Aug 14, 2010 4:27 pm

A crude draft of some of my notes on the FDD signal I/F is attached
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Re: Floppy Disk Drive Interface

Postby 1024MAK » Mon Aug 16, 2010 10:36 pm

Some info "lifted" from other threads which includes links...

From Question regarding STT images viewtopic.php?f=5&t=1241
Gunstick wrote:
Steem Authors wrote:There is one thing that I keep meaning to test, does it have details of how exactly the write protect bit in the status register works? TOS relies on it being up to date to detect media changes but lots of programs expect it to always be 0 even if the disk is write protected.


Ah the write protect bit... one of the big silly things in the ST

A floppy drive has the signals "disk change" and "write protect"
The ST only has "write protect"
yeah, so to detect disk change, a change on write protect signal is used.
when no disk is in the drive it signals "disk is write protected"
If the floppy disk is protected, no change occurs when swapping disks

WP status flopy status
HIGH non protected disk inside
LOW non protected disk is removed
LOW no disk in drive
LOW protected disk is inserted
LOW protected disk is in drive

Is that what you needed?

Georges

*
Steem Authors wrote:Hi Gunstick,

Thanks a lot for the info about write protect and read track corruption, hopefully I'll be able to knock up some sort of fake corruption for the next version of Steem.

As far as write protect goes, I'm not 100% sure but I think that there is always some sort of change in the write protect bit when a disk is inserted, TOS really relys on it in order to detect media change. It might be that when a disk is half-inserted in the drive it reads as read-write, but this is something I must check.

Anyway, media change seems to work so I'm not overly concerned with it. What is confusing me is that after the FDC performs a read sector command the write protect bit is always clear, even on a write protected disk. I really need to know how long it stays clear and what can return it to its correct state, is there anything in the book about that?

Cheers,
Russ

*
Gunstick wrote:
Steem Authors wrote:Hi Gunstick,

As far as write protect goes, I'm not 100% sure but I think that there is always some sort of change in the write protect bit when a disk is inserted, TOS really relys on it in order to detect media change. It might be that when a disk is half-inserted in the drive it reads as read-write, but this is something I must check.


No, the write protect works as I described. The book has another long section about how TOS recreates from one write protect signal again the mediachange and writeprotect status.

What the book says is the only WP problem is when swapping between protected disks. There will be no mediachange in that case. Why is that? Because the drive detects the button-push and puts the WP to low.

For the rest, TOS takes care (more or less successful) In old rom from $FC19B0 and blitterTOS at $FC1BC4 is the flopvbl routine doing it's tricks.
Every 8th VBL it checks the WP signal from the drive. With 2 drives at 50Hz that makes 2*8*1/50=0.32 sec delay.
The status are put in undocumentd variables they call wpstatus0, wpstatus1, wplatch0 and wplatch1
stored from $9B2 (old TOS) $9F8 (blitterTOS) on

wpstatus contains FF if the drive is protected
wplatch contains FF is during one scan period the WP was on

the bios MEDIACH call now does this:
if the time since last floppy access is >= 1.5 seconds AND if during that time the WP was at least once activated, THEN the change status is 1, in all other cases it's 0
From TOS 1.4 on that time is 1.15 seconds

Now if MEDIACH says there's a possible change, the BIOS reads the bootsector serial number to make shure. If they are the same, no disk change is assumed.

That explains some of my experiences with the ST. I apparently was able to change diskettes in less than 1.5 seconds! And the other problem with the serial number did make me some data corruption.

Georges

*
Steem Authors wrote:Hi Georges,

Thanks for the info, that's very interesting stuff. I have had problems with media change detection on my ST too, but I never thought it was so flakey. Steem actually just hacks this up by switching the write protect bit on and off after a disk is inserted, so that is why I never looked into it very much.

So TOS definitely expects the write protect bit to be up to date all the time, I wonder how long the FDC leaves it off after a read sector? I will write a test program sometime soon to find out, but this might not clear things up completely as it may be that the bit can be changed back to the real state in some way I haven't thought of.

Thanks again,
Russ

------------------------------
5min Sony HD floppy drive mod for ST/e
viewtopic.php?f=15&t=1515
------------------------------
viewtopic.php?f=3&t=8773&p=67828#p67828

ijor wrote:
ggn wrote:Well, just for the record, could you try to boot the images with tos 1.04 or even 1.02? My real ste (tos 1.06) sometimes had troubles identifying the correct disk when I changed them (indeed many of my disks had the fat trashed due to that).


Media change detection is broken on all 1.X TOS versions. Atari changed the code on each version but never made it correctly until TOS 2.

Under emulation could be even worse. Try enabling Pasti and try write protecting the images.

------------------------------
TOS 1.62 US
viewtopic.php?f=15&t=6088&p=69141&hilit=media+change+detection#p69141

ijor wrote:I Need a dump of the original TOS 1.62 US *and* TOS 1.62 uk.

Found a serious bug in the version that is available on the net. So I want to make sure that TOS version is actually the original one.

The bug is present in both US and UK versions. But strangley, Devpac crashes with TOS 1.62 uk under Steem. So the TOS version is easier for testing.

The fact that Devpac crashes with the Uk version, but not with the US one, makes me be even more suspicious about those TOS dumps.

Please make sure you have original ROMs before making the dump. If you don't know how to make a TOS dump, an utlity is available here:

http://homepage.mac.com/carlhafner/Atar ... mimage.zip

Thanks

*
ijor wrote:Thanks bripilot. It is the identical to the version available in the net. Still would like to get the Uk version when you can, Karlm.

After some investigation, the same bug seems to be present in all pre 2.x TOS versions. But the bug have no actual consequence on 1.0 or 1.2, only 1.4 and above (specially 1.62) are seriously affected.

Strange that the bug was never mentioned before. Somebody knows if exist some kind of release notes/addendum for TOS 2.X (as there are for TOS 1.4 and STe TOS)? Should be mentioned there as one of the fixed bugs.

*
ijor wrote:
karlm wrote:okeydoke.


Thanks a lot Karlm. It is different than the version I was using. Look that mine was corrupted. Now I have to check where I got it, just in case the corrupted version is at one of the main TOS sites.

Somebody has to make a database for official TOS roms including some kind of hash values (MD5 or better)!

bripilot wrote:Just wondering... what bug is it?


Btw, the bug has nothing to do with the corrupted image mentioned above. As said it's present in all pre 2.X versions.

The bug is that it will not detect a media change in one particular case. Specifically, it won't detect when you change the disk ... with the same disk. Oh, you ask, why I could care if I reinserted the same floppy. Well, you should care because the disk might have been modified in other computer.

Do the following test:

Format a disk. Create a small text file in the root directory with a short content, say "not modified". Read the text file. Now take the disk to the PC, open Notepad and modify the text for "yes modified". Reinsert the disk on the ST and reread the file. It will show "not modified" :)

You must use TOS 1.62, and possibly TOS 1.4. TOS 1.0 or 1.2 are not affected. They still have the bug, but they have no floppy cache so they will reread the files sectors anyway.

I'm not sure if you will see the bug if showing the file with the Desktop. I tried reading the file with my own software. The Desktop might possible read other data from the disk and then flushing the "old" cached sectors.

*
Greenious wrote:
ijor wrote:Btw, the bug has nothing to do with the corrupted image mentioned above. As said it's present in all pre 2.X versions.

The bug is that it will not detect a media change in one particular case. Specifically, it won't detect when you change the disk ... with the same disk. Oh, you ask, why I could care if I reinserted the same floppy. Well, you should care because the disk might have been modified in other computer.

Do the following test:

Format a disk. Create a small text file in the root directory with a short content, say "not modified". Read the text file. Now take the disk to the PC, open Notepad and modify the text for "yes modified". Reinsert the disk on the ST and reread the file. It will show "not modified" :)

You must use TOS 1.62, and possibly TOS 1.4. TOS 1.0 or 1.2 are not affected. They still have the bug, but they have no floppy cache so they will reread the files sectors anyway.

I'm not sure if you will see the bug if showing the file with the Desktop. I tried reading the file with my own software. The Desktop might possible read other data from the disk and then flushing the "old" cached sectors.


Actually, that is not a bug, it is a limitation in hardware that cause that, and it affects all versions of TOS.

The only way for Atari to determine if the disk has changed is to read the random serialnumber in the bootsector. If the serialnumber is the same, it assumes the disk has not changed.

It also causes problems with some formatters, that doesn't properly generate the serialnumber.

You can use "esc" to force a diskchange in desktop.

*
ijor wrote:
Greenious wrote:
ijor wrote:Btw, the bug has nothing to do with the corrupted image mentioned above. As said it's present in all pre 2.X versions.The bug is that it will not detect a media change in one particular case.


Actually, that is not a bug, it is a limitation in hardware that cause that, and it affects all versions of TOS.


No, it is a bug. Try with TOS 2.X and you will see the difference.

The only way for Atari to determine if the disk has changed is to read the random serialnumber in the bootsector. If the serial number is the same, it assumes the disk has not changed.


This is not accurate. The ST can detect if the disk was changed (and it indeed does). The bug is when trying to determine if the changed disk is the same disk or a different one. This would be exactly the same on the PC that has hardware support for media change.

*
Greenious wrote:
ijor wrote:
Actually, that is not a bug, it is a limitation in hardware that cause that, and it affects all versions of TOS.

No, it is a bug. Try with TOS 2.X and you will see the difference.


The limit is in the hardware. On other platforms pin 34 of the floppy interface is used to determine when a disk is inserted or not. That pin is not connected on Atari.

The only way for Atari to determine if the disk has changed is to read the random serialnumber in the bootsector. If the serial number is the same, it assumes the disk has not changed.

This is not accurate. The ST can detect if the disk was changed (and it indeed does). The bug is when trying to determine if the changed disk is the same disk or a different one. This would be exactly the same on the PC that has hardware support for media change.


Well, I can not say with with 100% certainty, but I believe Atari finally resolved this matter by always assuming the disk had changed. Like many "fixes" for this in earlier TOS that were released did.

*
ijor wrote:
Greenious wrote:The limit is in the hardware. On other platforms pin 34 of the floppy interface is used to determine when a disk is inserted or not. That pin is not connected on Atari.


We all know about the “DISK CHANGE” signal in pin 34. Still, the ST is able to detect by hardware (well, sort of) if the disk was removed or not. Do the following test:

Use TOS 1.0 or 1.02, won’t work with newer ones. Insert a standard disk, make sure it is write enabled (the test will fail if it is write protected). Open a window on the desktop for the directory of that drive. Now try clicking “ESC”. The window is refreshed, but the disk is NOT accessed.

As you can see, ESC didn’t force a media change, because the ST knows the disk wasn’t actually changed. If you now remove and reinsert the disk (or a different one, doesn’t matter) and hit ESC, the disk will be accessed. So the ST detected that the disk was removed.

How it does it without real hardware support? A simple trick. Periodically, every few Vertical Blank interrupts, TOS monitors the drive write protect signal. When you change a disk, you necessarily provoke toggles in the write protect signal. If TOS doesn’t see any toggle, it knows the disk wasn’t removed. This is of course not as good as real hardware support, it has some problems but it works pretty well.

Well, I can not say with with 100% certainty, but I believe Atari finally resolved this matter by always assuming the disk had changed.


Indeed. So it was a bug. Because it is wrong to assume, just checking the serial number in the boot sector, that the disk wasn’t changed. And this is not only because potentially you can have two different disks with the same serial number. Even if it is the same disk, you cannot be certain the disk wasn’t modified somewhere else (which could happen if you were transferring files from one computer to the other).

And this has nothing to do with having hardware media change detection or not. It is definitely a software bug. Exactly the same situation would happen in the PC. The hardware media change will tell you when the disk was removed, it won’t (obviously) tell if you reinserted the same or a different disk.

------------------------------
List of HD floppy disk drives useable with atari
viewtopic.php?f=15&t=7150&p=75117&hilit=media+change+detection#p75117

ppera wrote:There is another issue with standard floppies on Ataris:

Media change detection - Atari solved it little unusual, and today only few drives support it.
Point is in way how WP line works - if it will change status by disk change it is OK, otherwise Atari will not detect disk change what may result in data corruption on it. It stays for non-write protected floppies.

By non-supporting floppies it may be solved by simle logic - need to find point on floppy drive where disk insert is detected and combine it with WP line, and lead result of it to WP pin.

And to mention that there are ordinary ST's with HD floppy support...
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Re: Floppy Disk Drive Interface

Postby wongck » Tue Aug 17, 2010 11:53 am

Instead of doing this, Ynot just put it into the wiki pages.
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Re: Floppy Disk Drive Interface

Postby 1024MAK » Tue Aug 17, 2010 2:57 pm

wongck wrote:Instead of doing this, Ynot just put it into the wiki pages.

I will in due course.... :D
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Re: Floppy Disk Drive Interface

Postby robaq » Tue Oct 23, 2012 5:21 pm

1024MAK wrote:Atari External Floppy Disk Drive Adapter

Code: Select all

        Atari External Floppy Disk Drive Adapter

  ATARI       34 way IDC   Signal Name and Function
  STFM       connector for
14 pin DIN    Disk Drive
   N/U            1        Not used on Atari
   N/U *1 <----   2        Density Select
   N/U    ---->   4        In Use (tells drive to light it's LED)
   N/U    ---->   6        Drive Select 3 (DS3) - Not used on Atari
    4     <----   8        Index
    5     ---->  10        Drive Select 0 (DS0)
    6     ---->  12        Drive Select 1 (DS1)
   N/U    ---->  14        Drive Select 2 (DS2) - Not used on Atari
    8     ---->  16        Motor On
    9     ---->  18        Direction Select
   10     ---->  20        Step
   11     ---->  22        Write Data
   12     ---->  24        Write Gate
   13     <----  26        Track 00
   14     <----  28        Write Protect
    1     <----  30        Read Data
    2     ---->  32        Side Select
   N/U    <----  34        Ready / Disk Change - Not used on Atari
    3            *2        Ground (GND / 0V)
    7            *3        Ground (GND / 0V) / Density Select (see notes)

Notes
*1     Density Select is not normally used on Double Density (DD) drives.
       On some High Density drives this is an output from the drive to signal that a HD disk is in the drive.
*2     Connect pin 3 on the Atari 14 way DIN to the odd numbered pins 3 to 33 on the IDC drive connector,
       which are all Ground (GND / 0V) connections.
*3     On modified Atari's pin 7 of the 14 pin DIN is disconnected from ground and used for the Density Select
       signal from pin 2 of the IDC drive connector. On unmodified Atari's this is another Ground (GND / 0V)
       connection.

This is my 14 way DIN to 34 way IDC floppy adapter that I made up many years ago. I have not yet modified it to made it HD compatible, but will do in due course.
Note that the IDC connector "socket" on the cable at the stripboard end has the cable connected "upside down" compared to a standard "IBM PC" drive lead, so if you wish to copy this design, you will need to make up your own IDC ribbon cable drive lead (or modify a PC one). The red stripe indicates the core used for pin 1, but because the connections are reversed on the PCB connector, on the IDC cable "socket" the blue stripe is connected to what is supposed to be pin 1 on the IDC connector. I hope I have not confused the issue too much :lol:
So for example, the yellow wire (the one on the end, not the middle one) going to the 14 way DIN plug is "Side Select" and is connected to pin 2 on the 14 way DIN plug. The next wire, the white one is "Read Data", the next, (orange) wire is "Write Protect" etc...

Sorry for the huge quote.
Does this work with IBM PC floppy drives (without the option to put them in DD mode)?


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