ISA SCSI w/Floppy Controller

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ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-1-24 @ 07:08

My end goal here is to have more than two floppies (I want to have my 360kb + 1.44mb + gotek so I can access my physical media as well as avoiding wearing out my floppies)
Anyways I did some research and rummaging and I found that I had an AHA-1540B/42B (ISA SCSI with a bios from '88) that actually has an on-board standard FDC controller.

Supposedly it supports all the four standard floppy types, I have read the manual and reset all the jumpers (Making sure BIOS and FDC are enabled) but no matter what I do I can't seem to get it to detect any floppies.
BIOS shows up and scans for SCSI drives, so the card is working as much.

But I can't seem to get any life-signs from the FDC portion, not even if I disable the motherboard FDC or fiddle around with jumper settings.

Perhaps I'm missing something obvious here. I was assuming I could just connect them and configure the controller somehow (bios menu or something) but everything seems to be jumper based and I can't find any info on how to select the types (360, 1.44, etc). Even assuming it just auto-detects and configures drives I get no additional drives when in DOS. I'm not using any software drivers, could the FDC part possibly require that? (Then it wouldn't support booting, which is kinda odd in my book)
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Re: ISA SCSI w/Floppy Controller

Postby tayyare » 2019-1-24 @ 07:36

Cloaked Alien wrote:My end goal here is to have more than two floppies (I want to have my 360kb + 1.44mb + gotek so I can access my physical media as well as avoiding wearing out my floppies)
Anyways I did some research and rummaging and I found that I had an AHA-1540B/42B (ISA SCSI with a bios from '88) that actually has an on-board standard FDC controller.

Supposedly it supports all the four standard floppy types, I have read the manual and reset all the jumpers (Making sure BIOS and FDC are enabled) but no matter what I do I can't seem to get it to detect any floppies.
BIOS shows up and scans for SCSI drives, so the card is working as much.

But I can't seem to get any life-signs from the FDC portion, not even if I disable the motherboard FDC or fiddle around with jumper settings.

Perhaps I'm missing something obvious here. I was assuming I could just connect them and configure the controller somehow (bios menu or something) but everything seems to be jumper based and I can't find any info on how to select the types (360, 1.44, etc). Even assuming it just auto-detects and configures drives I get no additional drives when in DOS. I'm not using any software drivers, could the FDC part possibly require that? (Then it wouldn't support booting, which is kinda odd in my book)


Adding more than 2 floppy drives is not as trivial thing.

First of all, most floppy controllers (either part of an IDE multi I/O card or a SCSI controller) are just interfaces, and handled by the system BIOS which in almost all cases support only two floppy drives at best, if not a single one. BIOS in your SCSI controller card is only for the SCSI devices you connected to that card.

Here is a good read:

https://www.seasip.info/VintagePC/floppies.html

Don't get intimidated with electrical signal details in the beginning. It realy has good understandable information as it progressed.

You need to have special hardware and supporting software to make it work. It is definately not "plug and play".
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-1-24 @ 08:09

Hmm, alright, so if I disable the on-board controller and use the one on the SCSI card it'll be the System BIOS (It's a fairly modern Pentium 2-era mobo) that handles the floppy drive settings?

I kinda assumed that anything with a FDC interface just had it's own BIOS support for it, if that's not the case I guess I either have to make sure something has proper BIOS support for it or just simply go about the physical switch approach. Which would be fine to be honest. As long as I can use the Gotek together with the other two drives ^^
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-1-24 @ 08:38

Alright, so doing some more research it would seem that the absolutely best approach in my situation would simply to do the "Two Drive Monte"-switch as described in the link you provided =)
System never sees any more than two drives at a time and I'd retain maximum compatibility.

Next thing would be to research if I can do the selection jumper mod or if I have to bother with the actual floppy cable.

Thanks for the reply! Was really helpful!
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Re: ISA SCSI w/Floppy Controller

Postby eisapc » 2019-1-24 @ 09:03

Been there, done that, but can not remeber the dirty details.
Basically the secondary controller needs the option to set it to secondary I/O port (J7 on the 1542B). I am not sure if a dedicated driver was required, but surely these drivers exist (eg DC2.sys by TMC). Finally a little fiddling with drivparm and driver.sys was needed to set the floppy parameters instead of setting these in BIOS.
I need to check the details at home, but not sure where I stored the unit in question (Compaq Deskpro 286) and its surely at the bottom of a stack.
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-1-24 @ 09:32

Cheers. something called SDRIVE was mentioned and I'm certainly going to give that a whirl when possible. Although it might not make it possible for me to boot my Gotek it might at least make it very useable ^^
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-1-24 @ 16:27

Okay, so now I have tried disabling the internal FDC and just straight up connecting both my drives to the SCSI-card, great success! \o/

However now I have jumpered it to be a secondary controller, which makes the BIOS not recognize them (as expected).

I've only managed to find SDRIVE and it claims "Driver Not Loaded - No Operational Controller" and "Secondary Controller is not Operational" but I've ready not everybody has success with it so still not sure if the error is mine or software-wise =)
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Re: ISA SCSI w/Floppy Controller

Postby SirNickity » 2019-1-24 @ 18:34

I have nothing to add, just want to encourage the updates on this thread. This was something I didn't even know was possible, and I'm intrigued.
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-2-05 @ 19:36

Still haven't found a solution to this unfortunately. Would love to have my 1.44 + 360 + Gotek run at once, but I figure the best solution would be some way to simply switch between them mechanically.

Question: Would it suffice to make sure just one drive at a time has power? Or could switching power on/off while powered on damage drives / controller? If that's the case my easiest solution would be a modified floppy cable with a switch for the drive control line.

I wish those came ready made somewhere ^^
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Re: ISA SCSI w/Floppy Controller

Postby SirNickity » 2019-2-05 @ 19:50

Depends on the bus transceiver, I would think. I'm not particularly familiar with common IDE / floppy interface designs, but from a general electronics perspective...

A lot of digital inputs can be damaged if voltage is applied without being powered, but because of that, it's super common to harden external interfaces with series resistors, and protection diodes to Gnd and V+. Essentially, if there's +5V on the bus but no power, the resistor current-limits the stray voltage (to micro-amps, for e.g.), and the diodes shunt it to the drive's rails. Since there's not enough current to power the drive, it does nothing noteworthy.

Now, this may still interfere with the operation of other devices on the bus. It depends on whether the transceiver is truly high-impedance (open circuit) when powered off. It could present a parasitic load that affects the transition time, or signal level, etc. Pull-up / pull-down resistors may also present an unexpectedly high load on the bus if there are more devices than the bus is intended to support. (Although, apparently it's meant to drive four under certain circumstances, so three shouldn't be a problem.)

Grain of salt and all. This is all speculation based on other digital interfaces that I know better than the FDC. In the absence of any specific knowledge by more experienced hardware hackers, I would suggest the most reliable thing to do, by far, is to power the drive and use the select line to properly tri-state the bus transceiver when the drive is not being selected.
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Re: ISA SCSI w/Floppy Controller

Postby luckybob » 2019-2-05 @ 21:12

does your system support USB? If so, the quickest, cheapest option is a USB 1.44 floppy drive.

A 2nd option is a LS-120 drive. it puts the 1.44 floppy drive on IDE and subsequently leaves the gotek and 360 open for the actual floppy drives.
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Re: ISA SCSI w/Floppy Controller

Postby retardware » 2019-2-06 @ 02:13

Yes it is possible.
It is almost 35 yrs ago that I connected these 8" 1.2MB DSDD drives to my PC.
I used them to transfer some old CP/M stuff to MS-DOS. Xenocopy and Uniform were greeeaaattt utilities!
Some info about connecting floppies: https://www.seasip.info/VintagePC/floppies.html

Remember, in the 1970s it was common to have external drive enclosures, using the external Shugart ports on computer and drive enclosure.
(This straightforwardly answers your question regarding whether it is safe to have drives without power on the bus: Yes.)

Back then I had a lot of literature about undocumented DOS stuff.
If I remember correctly, the DOS drive parameter table (which is changed by drivparm/driver.sys) also contains a field for the drive's associated 765's base address, to deal with hardware using multiple disk controllers.
But now I seem unable to find the drive parameter table (DPT) data structure in the Web :(
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-2-06 @ 07:44

I know I can go the USB route, but a good part of this is the "making what I've got work" =D

The system in question is a Pentium 2 in a black ATX case, black 1.44mb drive, black 360kb drive, cd-rom, Gotek (w/FlashFloppy), etc.

Motherboard and BIOS supports 2 drives.

I do have a SCSI-controller in the system with a floppy interface that I've managed to configure in such a way that it's supposedly a secondary floppy controller. I've verified that if I configure it as primary and disable the onboard controller both drives work on it, but as soon as I configure it as a secondary controller I'm unable to access anything attached to it as it requires special drivers/software (if I understand it correctly)

Mind you I still haven't tried everything in the book. I've pretty much only tested SDRIVE and something else that refused to work. That was in DOS 7.1 though, I know have the system setup with a 6.22/7.10(Win98SE) dual-boot setup.

What I should do is connect the Gotek to the secondary controller and see if I can access it through specialised software/drivers, I just need to collect as much relevant software as possible. It's a shame that DC2.SYS that I keep seeing mentioned is nowhere to be found =/
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Re: ISA SCSI w/Floppy Controller

Postby luckybob » 2019-2-06 @ 08:16

The bios does not support >2 floppy drives is the real issue.

You will need to configure them manually in dos via "driver.sys"
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-2-06 @ 08:28

luckybob wrote:The bios does not support >2 floppy drives is the real issue.

You will need to configure them manually in dos via "driver.sys"


As I understand it I need some kind of driver that enables drive 3/4 as well.

It's a shame you can't just patch and re-flash bios to up it from 2 to 3 or 4 drive support ^^

Sadly, at the end of the day I still think the physical switch option will be the most compatible one. It just require a bit of work to construct a cable.
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Re: ISA SCSI w/Floppy Controller

Postby eisapc » 2019-2-06 @ 10:03

Cloaked Alien wrote: It's a shame that DC2.SYS that I keep seeing mentioned is nowhere to be found =/

Let me look at my archives. I received it again just weeks ago. There was some driver from Ultrastore as well to drive as third floppy.
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Re: ISA SCSI w/Floppy Controller

Postby Anonymous Coward » 2019-2-06 @ 14:55

You can get special controller cards with their own BIOSes to use four floppies on a PC. I have one of these cards, unfortunately I have never tried with more than two floppies at a time. I remember buying from JDRmicro, and the brand is "MCT".
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Re: ISA SCSI w/Floppy Controller

Postby eisapc » 2019-2-11 @ 19:08

Attached the DC2.sys I didnot test it myself, just forwarding if anybody is interested.
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-2-11 @ 21:04

Cheers!
Will give it a run when I have the opportunity =D
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Re: ISA SCSI w/Floppy Controller

Postby Cloaked Alien » 2019-2-12 @ 21:12

Hmm, you wouldn't happen to have a manual or reference config line or anything for that one? I'm afraid I'm at a total loss to what I should even do =/
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