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Floppy Disk Drives Interfacing

Crypticalcode0

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I am just wondering which is the most prevailing interface for a FDD?

I am doing this from memory so don't gun me down for a typo. ;)

Uneven numbered pins all are ground this is what is common on most standards.(yay signal grounds)
And all signals are inverted to Negative logic.

Modern Variable pinout
2 Reduced Write, Density Select
4, 6 N/C
8 IDX
10 MOTEA
12 DRVA, DRVB
14 DRVB, DRVA
16 MOTEB
18 DIR
20 STEP
22 WDATA, Write Data
24 WGATE, Write Enable
26 TRK0, Track 0
28 Write Protection
30 RDATA, Read Data
32 HSEL, SSEL, Header Select, Side Select
34 DSKCHG, Disk Change

Shugart
2 DCD, Disk Change Detect
3 Key
4 DS3, Device Select 3
6 INUSE,
8 Index
10 DS0, Device Select 0
12 DS1, Device Select 1
14 DS2, Device Select 2
16 MTRON, Motor on
18 DIR, Direction
20 STEP
22 WDATA, Write Data
24 WGATE, Write Enable
26 TRK0, Track 0
28 WPT, Write protect
30 RDATA, Read Data
32 SIDE1, Side/Header select
34 RDY, Drive Ready/disk Change

Edit: 5170 High capacity diskette drive
2 Reduced Write
4 Reserve
6 DS3
8 IDX
10 DS0
12 DS1
14 DS2
16 MTRON
18 DIR
20 STEP
22 WDATA
24 WGATE
26 TRK00
28 Write Protect
30 RDATA
32 Side 1 change
34 Diskette Change

Edit: Diskette Drive adepter 5.25
2,4,6, N/C
8 IDX Index
10 MOTEA, motor Enable A
12 DSB, Drive Select B
14 DSA Drive select A
16 MOTEB, motor enable B
18 DIR. direction stepper motor
20 STEP, step pulse
22 WDATA, write data
24 WE, write enable
26 TRK0, track 0
28 WP, write protection
30 RDATA, read data
32 Select Head 1
34 Unused

Which of these is more commonly found?
And is there another standard?
 
Last edited:

Chuck(G)

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Are you talking about the lines at the controller, or the lines at the drive? On the two where you show two motor enables, those are controller pinouts, peculiar to the IBM PC family. At the drive interface there is only one motor select--the "twist" in the cable for the second drive is what it makes it look as if the drive has two.

The others are drive pinouts. Out of the two remaining, the top is typical for 1.2MB and 1.44MB drives; the bottom one is used for older 360K and 720K drives, as they have neither density select (don't need them) and disk change(don't implement that, although some 3.5" ones do).

You left off several other variations. A lot of older 8-bit systems use pin 34 as a "drive ready" pin.

But even that doesn't scratch the surface. There is also a 26-pin 3.5" interface (Sony); there are various reassignments of pins on 3.5" drives for "host density select" and "media sense". Some 3-mode drives use pin 4 to switch between 1.44 and 1.3MB use...

And then there are 8" drives, with a wide variety of special pins (e.g. head load, sector, etc.) Older 8" drives may have many other unusual assignments, such as "seek complete". RWC/TG43 is generally only used on earlier 8" drives.

But generally speaking, the useful subset is the Shugart SA-450 interface, with 4 drive selects, one motor enable and no assignments to 2-4 and 34. 1.2M and 1.44M drives, will of course, need pin 2 "host density select" to call out the media type.
 

MikeS

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...generally speaking, the useful subset is the Shugart SA-450 interface, with 4 drive selects, one motor enable and no assignments to 2-4 and 34. 1.2M and 1.44M drives, will of course, need pin 2 "host density select" to call out the media type.
Umm, don't they also use pin 34 for DC (or RY in some non-PC applications)?
 

Chuck(G)

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Umm, don't they also use pin 34 for DC (or RY in some non-PC applications)?

Thought I'd mentioned that:

Me said:
A lot of older 8-bit systems use pin 34 as a "drive ready" pin.

I've also seen drives that can also be jumpered for "media type" (tell me what's in the drive) on pin 34 (or 2) as well.

Given that two of his pinouts were for PC controllers, I'm assuming that's what he's interested in. But maybe not.

The "ready" thing is important on a lot of 8-bit systems. Usually, the approach is to connect it to drive select, so the drive always looks ready. Sometimes this works; a lot of 3.5" drives, for example, block "index" until a drive actually comes ready.
 

Chuck(G)

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Again, are you talking about the signals at the controller, or the signals at the drive? For what hardware platform? For what years? For what kind of drive?

The interface has changed only in minor details since the Shugart SA-450. But AFAIK, there is no official "standard" other than the pro-forma one detailed by Shugart.
 

Chuck(G)

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But take a look at what he's got listed. His (1) and (4) are controller-side pinouts. No drive-side pinout separates motor enable like that, unless it's a "combo" (e.g. Teac FD505) drive, where there are two drives and only one cable.

(3) is close, but it's been convention to have 3.5" drives use media-density-select instead of host-density-select on pin 2, although some 3.5" drives can be jumpered to use pin 2 as a density input (early IBM PS/2 systems did it that way, which was why you'd see lots of DS2D floppies formatted as DSHD. Pin 2 for 3.5" floppies normally NC on PCs.

So, if we're talking about drives I'd have to say that (3) prevails with the proviso that 3.5" and 5.25" 360K drives generally ignore pin 2. So (4) is really the old 5150/5160 controller pinout. You can see that where they primarily differ is pin 2 and 34, which didn't come in until the 5170.

..and other platforms (e.g. Mac, Apple II, C64, etc.) are a completely different kettle of fish.

Further, on a PC, any single-drive select is going to involve DS2 only. So some late drives don't even have a drive-select jumper; DS1, DS3 and DS4 are no-connects.

As far as the Shugart, the full set of signals was never commonly used. NEC also had its own system for the PC98 platform.
 

Crypticalcode0

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Chuck if you know the other thread i am in then you would know i want to use run of the mill parts so yeah the most common PC parts that they have been throwing people to death with in the last 15 years.(a little less now then back then)

So i would like to know the most common FDD interface on those, I don't like the obscure that much.
 

Chuck(G)

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I don't think I've seen the other thread, so I'll go with this:

Most common drive interface (late legacy) the 5170, your No. 3.

Most common controller interface (late legacy), your No. 1.

Does anyone still make a modern (i.e. designed in the last year) PC with a legacy floppy interface?
 

MikeS

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What Chuck said, although I don't understand why #1 is "variable"; that's been the PC "standard" since the AT even though pins 2 and 34 are not used with all drives. Also, pins 12 and 14 are DS B and A respectively, not both.
 
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