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Is there a floppy DB25 standard wiring of any type?

alank2

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I'm going to be using a 3' all pins straight through DB25 serial cable between the Altair 8800C I built and a couple of floppy drives I'm going to build an enclosure for.

There are 14 signals I plan to have are ds1, ds2, ds3, ds4, motor, index, direction, step, write data, write gate, track 0, write protect, read data and side, which leaves 11 grounds out of the DB25.

My question is, of all the floppy drives using DB25, is there any sort of standard for which pins are which?
 

Chuck(G)

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Aside from a few laptops, the most common D-sub for floppies that I've seen is DC37. More than enough signals, with a few left over for power, should you decide to use them. Using IDC connectors is easy in this case--just take the 34 conductor ribbon cable and line it up in the IDC DC37 such that pin 37 makes with pin 34 on the cable and Bob's your uncle.
 

DeltaDon

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The Chicony MP975 used a internal/external 3.5" floppy module that could be connected via the serial DB25 when the CD drive was installed in the internal drive bay. But I doubt there was a standard other than what Chicony decided to cobble together.
 

Chuck(G)

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As I mentioned, some laptops used it. My old Gridcase certainly used a DB25 for its external floppy access.

Generally, I'm not a fan of using the 25-conductor DB shell for anything but RS232 interfacing. It's been abused to death, with IBM using it for parallel/printer port access, necessitating a special cable to get it to the normal 34-conductor "Amphenol blue ribbon" connector. Some budget SCSI controllers used it and who knows how many other devices used it as a connector--with the proponents blithely ignoring the fact that RS232C/EIA signal levels would destroy their devices, should a user mistakenly plug a piece of RS232 gear into the "other use" receptacle.

DC37 was widely used for floppies (just check the 5150 floppy controller, as well as the PS/2 and a whole host of other gear). It was also used for a few SCSI-controllers, mostly from Iomega, who used the DC37M as the host interface connector, so you're unlikely to mistake one for the other.
 

deramp5113

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I’ve seen the 50 pin Shugart 8” standard ribbon cable split in the middle and pressed into two DB-25 connectors which are then inserted in the cabinet rear panel. The external mating cable is made the same way, opposite DB-25 gender, of course.

Mike
 

Chuck(G)

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And there was the Xerox 820 8" floppy unit, for example, with two Shugart drives--terminated in a DC37 connector.

To answer the original question: There is no standard configuration for a floppy to use a DB25 connector.
 

alank2

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Thanks guys; I'm just going to assign the pins then. I'll begin with the floppy side and just see where they go. My goal is to just have a single DB25 that is easily mountable in the back of the 8800C. When I get it done, I'll post some pics.
 

Eudimorphodon

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FWIW, there may actually be a “semi-standard” for connecting a single floppy drive via DB-25 that dates to the 1990’s. There were several brands of laptops (the Dell CPx series is a common example) that allowed a floppy drive to be cabled to the parallel port, and said floppy drive was *not* a parallel unit, it was a real “normal” floppy hanging off a regular Floppy controller. Long and short of it is these laptops were equipped with a superI/O controller chip that multiplexed the pins of the connector between parallel port and floppy functions depending on whether a drive was detected.

I remember finding the data sheet for one of these chips once but I can’t promise it’ll be easy to find. Here’s a patent number:

US5535371A

for the invention, it has a pin out in it. I don’t know if all manufacturers were consistent but if they used the same interface chip I imagine it’d be close.
 

shirsch

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And there was the Xerox 820 8" floppy unit, for example, with two Shugart drives--terminated in a DC37 connector.

To answer the original question: There is no standard configuration for a floppy to use a DB25 connector.

I just finished building an adapter to interface my Xerox 820-II with a Gotek/FlashFloppy emulator. Works quite well and much quieter than that beast of a dual-8" drive enclosure! Fortunately the DC37 pinout is documented in the tech manual.
 

alank2

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Thanks Chuck - I can start with that pinout instead of just coming up with something no one has ever used!
 

alank2

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So it looks like I am going to use an IDC style 2x13 100mil header because that is what will fit in the drive enclosure I have. It does look like there is a standard for this - I found.

I need a DS0 and DS1 - was the DRVS on this used to select drives? Low=one drive and high=another? They didn't need to unselect them?

Would you recommend this layout? I won't be powering them so I'm thinking the VCC lines will be N/C. I also need a DS0 and DS1 so any thoughts on where I should put those?
PinPin
Name
Description
1VCCVCC +5V
2/INDEXIndex
3VCCVCC +5V
4/DRVSDrive Sel
5VCCVCC +5V
6/DSKCHGDisk Change
7RESReserved
8READYused only in older drives. In newer drives N/C.
9MEDIAused only in older drives. In newer drives N/C.
10/MOTEMotor Enable
11/REDWCDensity Select
12/DIRDirection
13RESReserved (Inuse)
14/STEPStep
15GNDGround
16/WDATEWrite Data
17GNDGround
18/WGATEWrite Gate
19GNDGround
20/TRK00Track00
21GNDGround
22/WPTWrite Protect
23GNDGround
24/RDATARead Data
25GNDGround
26/SIDE1Side 1 Select
 

Chuck(G)

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The question here is "Will anything with a DB25 other than your special floppy go kablooie if you plug it into your socket?".

I still don't understand your resistance to a DC37.
 

alank2

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Chuck - I can appreciate how standard it is, but the holes I have in both chassis will not support it. The rear of the Altair 8800 has 8 pre-cut slots for DB25 (which I can fit an IDC 26 in ), and the rear of the Drive enclosure I have had a SCSI 68pin connector that is even less wide than the DB25, but will still fit an IDC 26 without a shroud. I've found there is a Altair MiniDisk IDC 26 pin out so I may try to model after that.
 

Chuck(G)

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Well, there's also DB44 (high density) as well as a DA26HD if you need something smaller. Neither of which has any corresponding common peripheral connector. NB: The DA26HD is sometimes (erroneously) referred to as a DB26HD as here. The shell is "A" size, the same as the common DA15 sometimes used for joystick connections.
 
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