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few quick question on Commodore Colt

I bought 25 - 50 from bgmicro.com back in 2006. Maybe they still have some.

And yes I do have basically all of them still. Jammed somewhere in a storage unit. I'll try and keep an eye out.

For clarity (haven't been monitoring this thread) what I have are small card edge on one side, 34 pin female on the other. To make a cable made only to connect to 5 1/4" drives accept a newer 3 1/2" floppy (yes 3 1/2" floppies used to have card edge connectors).
 
vwestlife said:
Maybe Commodore followed the Amiga standard for the floppy drives on their PCs? The Amiga floppy cable has a twist, but it's in a different place than on regular PC floppy cables.
Click to expand...

None of my Amigas have a twisted cable.
I googled some images to make sure, but seems to be straight:
http://www.cbmfreaks.com/wp-content/uploads/2011/01/5.jpg
http://www.nathandumont.com/files/images/amiga500_inside.jpg

The PC10-III I had and the PC20-III I have now, also have no twist in the cable (even for 2 drives, they rely on the old drive select jumpers on the drive).
I tried with a generic twisted cable from some clone, and setting the jumpers to ds1 on all drives... That seemed to work as expected. The twist only affects the drive select thing, and that part seems to be standard.

What I have been able to dig up so far is that the system uses an FDC9268 controller chip, which is also used on the Amiga BridgeBoards: http://amiga.resource.cx/manual/A2088-A2286.pdf
These apparently use standard Amiga external drives, with a standard Amiga connector, as MS-DOS compatible drives (you can also do that without a BridgeBoard by the way. You can just load a device driver and use your internal/external Amiga drives for reading/writing MS-DOS floppies).

Which makes me wonder though... Why didn't it work when I just took an internal drive out of my Amiga and hooked it up to the PC20-III?
 
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Through a bunch of trial and error, I was able to successfully get both my 360K 5.25” and 720K 3.5” disk drive / 720K Gotek working together in my PC10-III. :)

First, let’s talk about the floppy disk cable itself. The PC10-III cannot use a twisted cable. The cable I ended up using has two 3.5” connectors and one 5.25” connector with a twist in the cable. The only thing I needed to do to the cable was straighten out the twist.



Second, none of the jumpers need to be changed.

Third, everything else needs to be configured via jumper settings on the drives themselves. Unless there are jumper pads that can be modified, it seems drives without jumper settings will only work as the A: drive.

The drives I successfully used for testing are the original Chinon FZ-502 5.25” 360K drive that came in the PC10-III, a Chinon FZ-357 3.5” 720K floppy drive, and a Gotek SFRM72-FU-DL 720K floppy emulator. During my testing, I was always using the 5.25” drive as the A: drive and the Gotek and 3.5” drive as the B: drive.

The jumpers on the 5.25” drive were set at default.



In order to get the Gotek working as drive B, I closed the JA and S1 jumpers. In order to get the 3.5” drive working as drive B, I closed the DS1, MD, DC, and TTL/C-MOS jumpers.



That’s it! Everything worked perfectly. :) Please let me know if you have any questions.

Heather
 
SkydivinGirl said:
The only thing I needed to do to the cable was straighten out the twist.
Click to expand...

Hum... I wonder if you just 'got lucky' with the Chinon FZ-357 (the additional jumpers you mention are not available on most drives, and may be important).
I haven't tried to 'untwist' my cable, but my cable has 4 connectors, so there's 3.5" and 5.25" before the twist, and again after the twist.
Should amount to the same thing.
Also, I wonder if untwisting the cable would have much of an effect, aside from swapping the meaning of the drive select jumpers.
That seems to be pretty standard, so I don't think Commodore deviated from that. If they did, then the drive select wouldn't have worked.

The idea with the twist is that all drives are configured as 'drive B:', and the drive that is connected after the twist is actually drive A: in practice, because the lines are reversed by the twist.

As far as I got with my experiments, hooking up drives before and after the twist, changing drive select jumpers etc, everything seemed to work as expected.

The TTL/C-MOS jumper in particular caught my attention: that seems to indicate different voltage levels for signaling.
Could it be that the Commodore controller uses a nonstandard voltage, which the drive logic does not respond to? Except for selected drives... apparently Chinons are what you often find in these Commodores. I'll have to check my Amiga drives again, I think at least some of them are Chinon, but I don't think they are FZ-357s. They are from A600s/A1200, so that is newer than the PC10/20-III and also the A500/2000 models.
Perhaps Commodore had already moved to a more standardized drive interface by that time...?
But who knows, some of my drives may have a TTL/C-MOS jumper, or at least some other jumpers I can experiment with.

Well, some areas I can explore :)
 
I went through many iterations of settings to get to this point. The only jumper that that actually changed on the FZ-357 was removing the jumper from MM and putting it on MD. Even though I changed the jumpers during my experimentation, all the other jumpers are in the location they were before I did anything. The drive was being recognized by the PC10-III with other settings, but the drive would not spin until after I moved the jumper to MD.

In regards to the cable twist, I tried the same drives both with and without the twist and was not able to get it working with the twisted cable. I couldn't tell you whether or not Commodore did anything weird, but there's no documentation that I could find so I'm relaying what worked and didn't work. If I 'got lucky' then so be it. I went through all this to help the original poster, not for my own needs. I'm not going to do any more testing.

Heather
 
Scali said:
Also, I wonder if untwisting the cable would have much of an effect, aside from swapping the meaning of the drive select jumpers.
Click to expand...
The twist also affects the MOTOR ON signals. See the diagram at [here].

SkydivinGirl said:
Even though I changed the jumpers during my experimentation, all the other jumpers are in the location they were before I did anything. The drive was being recognized by the PC10-III with other settings, but the drive would not spin until after I moved the jumper to MD.
Click to expand...
The jumper settings document at [here] shows that a lot of drives have a jumper setting that controls whether the spindle motor is driven by the controller's MOTOR ON signal or by the controller's DRIVE SELECT signal. The MM/MD jumper will be that spindle motor jumper on your drive.
 
modem7 said:
The twist also affects the MOTOR ON signals. See the diagram at [here].
Click to expand...

True, but it doesn't change the fact that the twist shouldn't change anything other than making signals for drive A go to the pins for drive B and vice versa (which is what the drive select jumpers on drives should be doing).
Namely, the pinout is like this:
10 - Motor A
11 - Gnd
12 - Drive select B
13 - Gnd
14 - Drive select A
15 - Gnd
16 - Motor B

Now, these 7 wires will be twisted backwards, so you get:
16 - Motor A
15 - Gnd
14 - Drive select B
13 - Gnd
12 - Drive select A
11 - Gnd
10 - Motor B

That shouldn't affect anything really, since no other signals are specific to a given drive.
(And my drive worked when I connected it after the twist, but jumpered it to drive select B).

So, if two drives work in the Commodore without a twist, where one drive is jumpered to A and the other is jumpered to B, then clearly the drive select and motor signals are on the standard pins.
Hence, the twist should also work as expected, and it should continue to work when both drives are jumpered to B.

The jumper settings document at [here] shows that a lot of drives have a jumper setting that controls whether the spindle motor is driven by the controller's MOTOR ON signal or by the controller's DRIVE SELECT signal. The MM/MD jumper will be that spindle motor jumper on your drive.
Click to expand...

Now this may actually be an explanation why my drives were not spinning up, even though the led indicated that it had indeed received a command.
I will give it another try next month, see if I can find a floppy drive with such a jumper, and see if that solves my issue.
 
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SkydivinGirl said:
but the drive would not spin until after I moved the jumper to MD.
Click to expand...

Yes, very helpful information. The spinning problem is what I could not fix during my experiments.
We may be on to something.

SkydivinGirl said:
I'm not going to do any more testing.
Click to expand...

No problem, thanks for your efforts! It has given us some new information.
I know how annoying it is to take apart these old computers, with annoying cables that don't fit the way you want etc... Then having to disconnect, re-jumper, reconnect, boot up etc...
Which is why I gave up eventually.

But, with this new information I'll be giving it another try next month. Because I'm the kind of guy who wants answers and explanations. And we now have a few working theories as to why drives may or may not work in a PC10/20-III/Colt.
If I can get a 3.5" drive working with 'MD' setting or with a given TTL/C-MOS setting, then that clears that up.
I will also try to get a definitive answer on the cable twist while I'm at it.
 
Scali said:
Now this may actually be an explanation why my drives were not spinning up, even though the led indicated that it had indeed received a command.
Click to expand...
On a lot of drives, the LED only indicates that the drive is 'selected' (via the DRIVE SELECT pins), with the MOTOR ON pin not affecting the LED in any way.

Scali said:
True, but it doesn't change the fact that the twist shouldn't change anything other than making signals for drive A go to the pins for drive B and vice versa
Click to expand...
But it does.

Looking at only the signals being swapped, it it easy to think, hey, IBM are just swapping the A drive specific signals with the B drive signals. Simple.
But when you look a bit deeper, where the signals go to on the drives, the situation with the MOTOR ON signals is not like that.

Looking at the diagram [here], if the twist was removed:
1. The MOTOR A signal from the controller (pin 10) will go to the DRIVE SELECT 0 pin on the drive (pin 10); and
2. The MOTOR B signal from the controller (pin 16) will go to the MOTOR ON pin on both drives (pin 16).

Scali said:
So, if two drives work in the Commodore without a twist, where one drive is jumpered to A and the other is jumpered to B, then clearly the drive select and motor signals are on the standard pins.
Click to expand...
But maybe the A drive used had been reconfigured at some point, just like what Heather did; ignore the MOTOR ON pin; drive the motor from DRIVE SELECT instead.

Scali said:
I will also try to get a definitive answer on the cable twist while I'm at it.
Click to expand...
The subject twisted cable is for the IBM PC family. Many clones use the same cable, in the same way. But there are variations. There was someone on this forum that discovered that their clone used the twisted cable, but the A drive is before the twist and the B drive after the twist! Some clones, such as Wang, use a straight-through cable.

I wonder what Commodore supplied from the factory.
 
modem7 said:
There was someone on this forum that discovered that their clone used the twisted cable, but the A drive is before the twist and the B drive after the twist!
Click to expand...

That was me, discovering that after much frustration in trying to get a B: drive installed in my Compaq Deskpro SB. It originally came with a straight-thru floppy cable with no B: drive connector. Replacing that with a standard dual-floppy cable yielded confusing results until I realized what you noted above. Essentially, the cable is already "pre-twisted" on the motherboard, and then the cable "un-twists" it for the B: drive!
 
modem7 said:
But it does.

Looking at only the signals being swapped, it it easy to think, hey, IBM are just swapping the A drive specific signals with the B drive signals. Simple.
But when you look a bit deeper, where the signals go to on the drives, the situation with the MOTOR ON signals is not like that.

Looking at the diagram [here], if the twist was removed:
1. The MOTOR A signal from the controller (pin 10) will go to the DRIVE SELECT 0 pin on the drive (pin 10); and
2. The MOTOR B signal from the controller (pin 16) will go to the MOTOR ON pin on both drives (pin 16).
Click to expand...

Ah yes, I see what you mean... The controller pinout does not necessarily match entirely with the drive pinout... which explains why the controller only has support for 2 drives, but many drives can also be configured as a 3rd or even a 4th drive (which works fine on an Amiga btw).

Well, regardless, I didn't even get my drive working as a single drive on the untwisted part of the cable yet. So I'll have to try that first. If that works, I can see what happens on other positions on the cable.

But maybe the A drive used had been reconfigured at some point, just like what Heather did; ignore the MOTOR ON pin; drive the motor from DRIVE SELECT instead.
Click to expand...

My theory is that the motor on is not used by the Commodore controller at all, and their drives have to use motor-on-drive-select configuration by default, else they won't work.
Since most drives/clones don't use this method, plugging in any random drive won't work. The led will come on, but the motor won't spin up, because the motor on signal is never activated.

I suppose nonstandard signaling on these lines may indeed have an effect on how the twist behaves. Although if my theory is correct that the motor on is never actuated, then that would mean the twist wouldn't have an effect on the PC10/20-III specifically.

I wonder what Commodore supplied from the factory.
Click to expand...

My first PC was a new PC10-III, bought in 1988 I believe, configured with 2x5.25" using a straight cable. I later placed the B-drive in my 386SX without a problem (if it indeed needed motor-on-drive-select, then that makes sense, it would be compatible with more standardized controllers).
This PC20-III is secondhand, but I have no reason to believe it has been modified in any way. It has a straight cable with only two 5.25" style connectors, just like my PC10-III did. It also still has the original WD 20 MB disk. There were no additional cards or anything installed.
The floppy drive is a different style than the ones in my PC10-III, but it looks the same as the one on various pictures of PC10/20-III systems on the web, so I suppose it's just from a different batch.
This is what my PC10-III looked like: http://file1.npage.de/000872/95/bilder/commodore_pc10_iii.jpg
And this is what my PC20-III looks like: http://www.richardlagendijk.nl/foto/cip/computer_pc20iii_01.jpg
 
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modem7 said:
The jumper settings document at [here] shows that a lot of drives have a jumper setting that controls whether the spindle motor is driven by the controller's MOTOR ON signal or by the controller's DRIVE SELECT signal. The MM/MD jumper will be that spindle motor jumper on your drive.
Click to expand...
Thanks for that! Without a manual for some of this stuff, it's very difficult to figure out what the settings are. I appreciate the information! :)

oblivion said:
My fz-354 doesn't have a jumper for an MD setting. Just mm or does removing the jumper from mm make it md?
Click to expand...
I honestly don't know but mine needed to be jumpered since it was there. Without a manual, it's difficult to tell but there's nothing stopping you from trying. It's very possible that you may need to make a modification on the floppy drive's PCB.

Scali said:
No problem, thanks for your efforts! It has given us some new information.
Click to expand...
Sorry about my earlier comment about doing any more testing. You got me a bit angry with your 'got lucky' comment. I put a lot of time and effort into figuring this out and your comment belittled the hours of work that I put in on this to help a member of the community. Nobody else got this far and the information I supplied seems to have helped.

I will be happy to do a little more experimenting if someone has a configuration they would like me to test.

Thanks,

Heather
 
SkydivinGirl said:
Sorry about my earlier comment about doing any more testing. You got me a bit angry with your 'got lucky' comment. I put a lot of time and effort into figuring this out and your comment belittled the hours of work that I put in on this to help a member of the community. Nobody else got this far and the information I supplied seems to have helped.
Click to expand...

Sorry, that is not how I meant it.
I meant to say that you were lucky that you had the Chinon drive to test with, because it has quite a few jumper options.
I mainly tested with an Epson drive from my Philips P3105, which only has a drive select jumper, as far as I recall. In which case, no matter what I do, I probably will not be able to make it work (unless it is as simple as just bridging the drive select and motor on pins... but I would never have figured that out, not knowing that some drives have jumpers to do that).

Some of the Amiga drives have a few cryptic jumpers as well, but at that point I did not feel like experimenting with those fiddly jumpers anymore. I had already spent a lot of time just getting the right cables (had to rig up a power cable too, since it only has 5.25" molex).
Now that I know you successfully got the Chinon working, and I know what jumper settings you used, I will get back to that later.
 
Scali said:
Sorry, that is not how I meant it.
I meant to say that you were lucky that you had the Chinon drive to test with, because it has quite a few jumper options.
Click to expand...
Thanks Scali. I appreciate the clarification. Text can always be misinterpreted, that's why I use lots of smileys to try to show the sentiment behind my words. I totally agree that having the Chinon with all the options was a bit lucky. It was also lucky that I even had a 720K 3.5" drive to test because out of all my drives, this was the only one. ;) :thumbsup:

I'll be interested to hear your results. :)
 
I have tried to look for some pinout information...
So far I have found that the floppy controller chip is an FDC9268.
This is also used on some Amiga BridgeBoards: http://www.amiga-stuff.com/hardware/fdc9268.html
That is interesting, since these BridgeBoards would connect to standard Amiga drives.
So I looked up the pinout of Amiga, and found this:
External_drive_wiring_V2a.png

As you can see, the external port is basically just the same signals as a regular 34-pin internal connector, but routed through a D23 connector.
However, you can also see that there is only one motor on line, and it is connected to pin 16. Pin 14 is not used.

With this configuration you would indeed need to combine drive select with motor on to make all 4 drives work.
Now, if the Commodore PC10/20-III/Colt use the same controller, it might mean they only have one motor on line as well, or even none at all.
And that would explain why the drive needs to work with the drive select instead of motor on.
I wonder what would happen if you'd just connect pin 10 to pin 14 yourself.

Oh well... I will investigate this theory later :)

Edit:
Some more info... Datasheet is here: http://www.datasheet4u.com/datasheet/F/D/C/FDC9268_StandardMicrosystems.pdf.html
Which tells us that it is an integrated version of the FDC765A and an FDC926B.
The FDC765A is a floppy controller chip, which in itself is a clone of the Intel 8272: http://www.intel-assembler.it/portale/5/intel_8272_floppy_disk_controller/tecnical_manual.asp
So that should be what it is compatible with...
Which does not make use of separate MOTOR A and MOTOR B signals. So it is not compatible with the later standard of floppy controllers, and the twist may have some unexpected results.
And here is some more information on floppy cables and the differences between drives and controller pinouts, and the use of the twist: http://pinouts.ru/Storage/InternalDisk_pinout.shtml
 
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