Adding a 5.25" to Commodore PC20-III

[Overmann]

Hello,

I am trying to add a second floppy drive to my machine. The one it came with is a 720kb 3.5" drive. I have three 5.25" drives but due to the shortness of the flopyp drive cable in the machine I am only able to test one of them, an Epson SD-680L. It is discovered as B: by the machine but does not read disks at all. No motor action. It seems to me that the machine might only support real 360kb drives, and mine are all 1.2mb drives. Also, I see that commodore sold kits for upgrading and doing so without a kit can be tricky. The 720kb drive in my machine has an adapter connected between the cable and the drive with jumpers on it. As far as I can tell the 5.25" drives that came in the machine does not have such an adapter, so I'm hopefull that I might be able to find a compatible drive without to much trouble. The other drives I have are Teac FD-55GFR and Epson SD-700, both 1.2mb drives.

Does anyone know how I would go about upgrading with a second, 360kb 5.25", floppy drive in my machine?

 

[Xacalite]

You definitely need a 360KB drive.
1.2MB drives can't work at all with a double-density FDC.

 

[archeocomp]

Not only that you need double density drive and diskettes, there is also problem that you have already discovered. No motor action. On board floppy controller does not use standard "motor-on" signals, rather only drive select. The drive has to be able to start motor based on this signal. I do not own PC20-III anymore but I recall I had the same problem.

 

[Overmann]

Phew, damn. I have a 286 planned, perhaps I'll save my dual floppy plan for that then. I'll keep looking for a compatible drive, but I guess it could take a while. Thank you for helping me out!

 

[SkydivinGirl]

I built one of Sergey's ISA floppy drive controllers to use in my PC10-III. It will allow you to use larger floppy drives and it also gives you another serial port.

Heather

 

[Overmann]

I built one of Sergey's ISA floppy drive controllers to use in my PC10-III. It will allow you to use larger floppy drives and it also gives you another serial port.

Heather

I thought it was impossible to disable the built in floppy controller. How did you get it to work?

 

[fatwizard]

I have a Commodore PC10, and the floppy cable has no twist, so the drives must be jumpered as DS0, or DS1 for the second drive. Mine also had a 720K drive installed, and the ribbon cable adapter for it has pins 12 and 16 jumpered together to start the motor with the drive select signal.

 

[archeocomp]

I thought it was impossible to disable the built in floppy controller. How did you get it to work?

BIOS on Sergey's card takes over the control of floppy. All that is needed is to jumper the card to another (secondary) FDC address and set BIOS accordingly. But you will get "drive A: error" message on cold start, as the CBM BIOS is always checking for drive A: attached to on-board controller. BTW I have patched the CBM BIOS to get rid of this message.

https://www.vogonswiki.com/index.php/Floppy_controller

BTW I did not use Sergey's FDC card, only Sergey's BIOS. I used GoldStar Prime 2C card, as it can be configured as secondary. Moreover I got additional serial and parallel ports and XT-IDE-CF on this single card.

 

[SkydivinGirl]

@Overmann

See archocomp's answer. You could probably keep a smaller drive connected to the original controller keep the A: error from popping up but I haven't tried.

@archeocomp

I hadn't seen someone use Sergey's BIOS with another card before. If you can find one, the GoldStar Prime 2C seems like a great way to go. Since the PC10-III has a built-in parallel port, just getting the high-speed UART serial port from Sergey's card was a good enough bonus.

Heather

 

[archeocomp]

To complete the information I used ethernet card with boot ROM in other slot, That way I had network with two serial, two parallel ports, 1.44MB drive and CF card, in just two slots.

 

[Overmann]

I have a Commodore PC10, and the floppy cable has no twist, so the drives must be jumpered as DS0, or DS1 for the second drive. Mine also had a 720K drive installed, and the ribbon cable adapter for it has pins 12 and 16 jumpered together to start the motor with the drive select signal.

I did not know that. Thanks! Good to know! I was wondering how the motor started in this setup.

@Overmann

See archocomp's answer. You could probably keep a smaller drive connected to the original controller keep the A: error from popping up but I haven't tried.

@archeocomp

I hadn't seen someone use Sergey's BIOS with another card before. If you can find one, the GoldStar Prime 2C seems like a great way to go. Since the PC10-III has a built-in parallel port, just getting the high-speed UART serial port from Sergey's card was a good enough bonus.

Heather

I have to have a think about my options. I really thought there were none regarding the floppy controller so this is all great news!

To complete the information I used ethernet card with boot ROM in other slot, That way I had network with two serial, two parallel ports, 1.44MB drive and CF card, in just two slots.

I'm pretty new to 8bit IBM compatibles. What do you use the ethernet with bootrom for? urrently I just have a controller card in mine, with gameport, serial and parallel because I needed a nine pin serial port for my mouse. I ould not get the onboard mouse port to work with my 1354 mouse, and the manual states that the mouse port is microsoft compatible but I don't know what that means. It won't take any of my serial mice.

I have a 8087 on the way as well but I understand that it's pretty much useless. I was hoping MS Flight Simulator or similar games would take advantage. Not to derail the discussion, but do you guys have any other interesting upgrades to recommend? Currently I am thinking about EGA-card (but I have no EGA monitor yet), an adlib, an IDE-controller and now a floppy controller. As you know the machine has very limited slots, so I would have to chose wisely. The controllercard that I have in there now would obviously go.

 

[Overmann]

BTW I did not use Sergey's FDC card, only Sergey's BIOS. I used GoldStar Prime 2C card, as it can be configured as secondary. Moreover I got additional serial and parallel ports and XT-IDE-CF on this single card.

Excuse me, but did you use Sergey's BIOS on a different card? How did you get it flashed to the Goldstar card? And how do you set the goldstar card as secondary. I have one of those but can't see an obvious way to get that done. Would that keep both floppy controllers active? IS it just a matter of changing the address of the goldstar's floppy controller? Do you have a special 8bit ersion of the card? Mine is 16bit.
And lastly, will the IDE part of the card work as well or is that what requires the 16bit bus?

 

[archeocomp]

Network card makes it possible to use http://www.brutman.com/mTCP/ that way, you have always correct real time (NTP) and can backup/store files (FTP server) conveniently over network from your home PC.

Sergey's BIOS was hosted in a ROM socket on ethernet card. Many ethernet cards have boot ROM socket that can be used for bios ROMs.
https://en.wikipedia.org/wiki/Network_interface_controller

Does your Prime 2 card have jumpers? Show us a pic or search for your card on internet, surely you will find how to jumper it to secondary floppy port. Both floppy controllers will be active. But Sergey's BIOS will only care for the one you configure it for. These cards are 16-bit but only for IDE HDDs, all the rest function require just 8-bit ISA bus portion. So it will work even in 8-bit XT computer.

 

[Overmann]

I made a mistake. The card I have is a Prime 2, not a prime 2C. It's one like this:

I do also have a winbond like this one:
Ebay link

I have several old ISA network card as well that I've not looked twice at. I'll have to see what they are. Perhaps they are more useful then I thought! mTCP sounds great, and I thought ftp on an 8088 was completely out of the question. This is going to be a much sweeter machine then I first envisioned. :D

 

[archeocomp]

I would certainly give this card a shot. J2 seems like it might set floppy controller for secondary address. But I am not sure about differences between Prime 2 and 2C..

I prefer Realtek 16-bit network cards, as I know which driver to use, but some other might work too. I seem recall I got Davicom 16-bit, Compex 16-bit, some NE2000 8-bit compatible and BC912 work. Someone posted here success about 3Com 3c509 in 8-bit PC. Again many of network cards are 8-bit friendly.

 

[KenEG]

I have a 8087 on the way as well but I understand that it's pretty much useless. I was hoping MS Flight Simulator or similar games would take advantage. Not to derail the discussion, but do you guys have any other interesting upgrades to recommend? Currently I am thinking about EGA-card (but I have no EGA monitor yet), an adlib, an IDE-controller and now a floppy controller. As you know the machine has very limited slots, so I would have to chose wisely. The controllercard that I have in there now would obviously go.

I would skip EGA and find an 8-bit capable VGA card. You can then pick up a used 4:3 LCD at a thrift store and you are in business. You can still use EGA modes. In my Colt, which I think is the same as the PC20-III, I have a VGA card and a Sound Blaster. I haven't decided what to put in the 3rd and last slot yet. I have an old 20MB drive in it using the onboard controller. The options I have considered are.

XT-IDE with or without the 20MB drive active
Network card
expanded memory

I may just leave it alone because it replicates the first PC compatible I owned.

 

[Overmann]

I would certainly give this card a shot. J2 seems like it might set floppy controller for secondary address. But I am not sure about differences between Prime 2 and 2C..

I prefer Realtek 16-bit network cards, as I know which driver to use, but some other might work too. I seem recall I got Davicom 16-bit, Compex 16-bit, some NE2000 8-bit compatible and BC912 work. Someone posted here success about 3Com 3c509 in 8-bit PC. Again many of network cards are 8-bit friendly.

That is great! I will give the controller card a spin in the coming days. I think atleast ONE of the ISA network cards I have is a realtek.

I would skip EGA and find an 8-bit capable VGA card. You can then pick up a used 4:3 LCD at a thrift store and you are in business. You can still use EGA modes. In my Colt, which I think is the same as the PC20-III, I have a VGA card and a Sound Blaster. I haven't decided what to put in the 3rd and last slot yet. I have an old 20MB drive in it using the onboard controller. The options I have considered are.

That's not a bad idea. I already have a very nice Nokia CRT monitor. Will a VGA graphics card be faster then the onboard chip when doing CGA? Or faster then a EGA card when doing EGA? I'm running it in monochrome at the moment as I can't seem to get my 1084S monitor to display the CGA correctly.

 

[KenEG]

I'm not sure about speed, but is that really a concern on these machines? With both 7.16 and 9.54 MHz modes available you can usually select a speed that works for any software that you would run on an 8088. I remember that my original Colt spent most of it's time at 9.54 MHz.

 

[Overmann]

I wanted to add a little update here. I have been trying to get my controller card working but I can't get it to handle both drives at the same time. I spent a couple of days trying different adresses and modes and drives but eventually had to give up. I'll see if I can find an original drive for a reasonable price, or one that is compatible with the onboard controller, or I might give a prime 2C a go. Those are affordable

HOWEVER now my 3.5" drive won't format 720kb disks anymore. It just formats 360. If I try to force it (format a: /F:720 or somesuch command) it tells me that the parameters are incompatible. Does anyone know what happened?

 

[Miggy]

I also have a PC20-III since a couple of months and noticed the same (small) problem with the 3.5" drive. It came with the 3.5" as the A:-drive and a 5.25" as B:-drive.

The 3.5"-drive reads 720 KB without problems and also has no problems writing to an already formatted 720 KB disk, but formatting is/was a no go: only 360 KB (format a: /f:720 did indeed not help). I was able to work around the problem by using "drivparm" in config.sys and can now format 720 KB disks

I haven't paid much attention to what a more definitive solution would be, as this works quite well for me. Might be looking into it later on, if ever. Maybe it's OS-related (I use DR-Dos 7.03), maybe it's the settings on the small pcb between the flatcable and the drive, maybe it's normal behaviour.

Oh, the computer came with a 3.5" drive factory installed as A:-drive: the seal of the case was still intact.