My SD-CF bridge was in a type I packaging and it only functioned at 3.3V, so I needed to use a IDE to CF adapter that has a voltage regulator to step down the v5 hard drive power to v3.3.

I hear there are SD-CF bridges that use the Type II packaging and might have a voltage adapter on board because they work at 5V.

They also make other IDE-CF adapters with other circuitry to step down the voltage. They are cheaper. I don't know if that would work for you.

douglar wrote on 2026-01-06, 19:01:

My SD-CF bridge was in a type I packaging and it only functioned at 3.3V, so I needed to use a IDE to CF adapter that has a voltage regulator to step down the v5 hard drive power to v3.3.

I hope you're aware that only changes the supply voltage, the bridge will still be receiving 5V on the IO lines since they're not filtered at all.

jmarsh wrote on 2026-01-06, 21:13:

douglar wrote on 2026-01-06, 19:01:

My SD-CF bridge was in a type I packaging and it only functioned at 3.3V, so I needed to use a IDE to CF adapter that has a voltage regulator to step down the v5 hard drive power to v3.3.

I hope you're aware that only changes the supply voltage, the bridge will still be receiving 5V on the IO lines since they're not filtered at all.

Not sure what you are getting at. Would you please elaborate?

If you look at the SD to 40 pin IDE adapters, you will see that there is a voltage regulator for the FC1307 chip, but 40 pin IDE signals go directly to the chip.

I imagine that this is the same thing, just in a couple different parts.

douglar wrote on 2026-01-06, 21:41:

Not sure what you are getting at. Would you please elaborate?

Compact flash cards must be designed to work at both 3.3V and 5V, as per the CF specification. So they're always safe to connect to IDE.

If an SD<->CF adapter only works with a 3.3V supply then it was obviously only designed to work in a 3.3V environment. But IDE IO signals are 5v, so by connecting that adapter to an IDE port you're effectively overvolting it (regardless of the supply voltage). There's a good chance the IO drivers will eventually get burned out. Level shifters would be required on all the IO pins but seeing as they were too cheap to even include a voltage regulator for the supply I would guarantee they're not present.

In my case the PCMCIA card has no jumpers, neither has a CF-SD adapter. I don't have an explicit IDE interface in this construction. But! Could it be, that Toshiba t1950ct doesn't provide one of the power supplies required by the PCMCIA (or CF-SD? One of them is probably passive) adapter? AFAIK the PCMCIA standard was still evolving in the mid 90ties...

Update: looking at the Table C-16 PC Card Slot Connector Pin Assignments (68-pin) of the "Toshiba T1950CT Maintenance Manual", I see that pins 43 and 57 are not connected. And according to https://vikant.com/PCMCIA-SRAM-Card.pdf they are Voltage Sense Signal 1 and 2 correspondingly. Could this be the missing part?

jmarsh wrote on 2026-01-06, 22:55:

If an SD<->CF adapter only works with a 3.3V supply then it was obviously only designed to work in a 3.3V environment.

I don’t know about that. All of the FC1307 chips I’ve seen take 5v ide signals without level shifters.

douglar wrote on 2026-01-06, 23:55:

I don’t know about that. All of the FC1307 chips I’ve seen take 5v ide signals without level shifters.

The "FC1307" is likely a 5V tolerant FPGA. The onboard voltage regulator is mostly for the SD card because they only work at 3.3V. There's no guarantee the same chip is used inside your SD/CF adapter, especially since it doesn't work with a 5v supply.

atar wrote on 2026-01-06, 23:27:

In my case the PCMCIA card has no jumpers, neither has a CF-SD adapter. I don't have an explicit IDE interface in this construction. But! Could it be, that Toshiba t1950ct doesn't provide one of the power supplies required by the PCMCIA (or CF-SD? One of them is probably passive) adapter? AFAIK the PCMCIA standard was still evolving in the mid 90ties...

Update: looking at the Table C-16 PC Card Slot Connector Pin Assignments (68-pin) of the "Toshiba T1950CT Maintenance Manual", I see that pins 43 and 57 are not connected. And according to https://vikant.com/PCMCIA-SRAM-Card.pdf they are Voltage Sense Signal 1 and 2 correspondingly. Could this be the missing part?

Nice find! Could be they took a short cut assuming that all CF cards will work at 5v, which has been my experience, with the exception of the Type I SD-CF bridge. Can your adapter take a Type II size? Those bridges might work better for you. Or do you have a read CF that you can test with to verify that the adapter works at all?

jmarsh wrote on 2026-01-07, 00:03:

douglar wrote on 2026-01-06, 23:55:

I don’t know about that. All of the FC1307 chips I’ve seen take 5v ide signals without level shifters.

The "FC1307" is likely a 5V tolerant FPGA. The onboard voltage regulator is mostly for the SD card because they only work at 3.3V. There's no guarantee the same chip is used inside your SD/CF adapter, especially since it doesn't work with a 5v supply.

I looked at the firmware. It was an FC1307 chip. Sinitechi 1.2

But I appreciate the discussion, my electical knowledge is pretty weak.

atar wrote on 2026-01-06, 17:05:

This matryoshka-like construction works with no problem in a P3 Thinkpad a30p laptop under Linux.

Try using this machine to create a FAT16 partition on the drive. The SD->IDE adapters try to load a FAT partition to know what C/H/S values to emulate and they can get stuck (returning ATA IDENTIFY information for every read request) if they can't find one.

douglar wrote on 2026-01-07, 00:05:

Or do you have a read CF that you can test with to verify that the adapter works at all?

Hey, nice avatar. I use dosboot to boot NetBSD 😀. Do you mean to test it in 486 (because it works in i686, as in the original post)? Unfortunately I don't have any CF-cards and this is the question: are there any which support different voltages? And FWIW support different bus modes (16 bits vs. 32)?

jmarsh wrote on 2026-01-07, 00:16:

Try using this machine to create a FAT16 partition on the drive. The SD->IDE adapters try to load a FAT partition to know what C/H/S values to emulate and they can get stuck (returning ATA IDENTIFY information for every read request) if they can't find one.

Good point. Checked it and the FAT16 partition seems to be already there:

1 fdisk -l /dev/hde
2
3Disk /dev/hde: 252 MB, 252968960 bytes
416 heads, 32 sectors/track, 965 cylinders
5Units = cylinders of 512 * 512 = 262144 bytes
6
7   Device Boot      Start         End      Blocks   Id  System
8/dev/hde1   *           1         965      246989+   6  FAT16

Tried a few different SD-cards. They all work in the i686 laptop and do not work in i486. Also the i686 says:

1hde: FC-1307 SD to CF Adapter V1.5, CFA DISK drive
2hdf: FC-1307 SD to CF Adapter V1.5, CFA DISK drive
3ide-probe: ignoring undecoded slave
4ide2 at 0x4100-0x4107,0x410e on irq 11
5hde: max request size: 128KiB
6hde: 3854336 sectors (1973 MB) w/8KiB Cache, CHS=3823/16/63
7hde: cache flushes supported
8 hde: hde1
9ide-cs: hde: Vpp = 0.0

The geometry is different and correct for all the cards, but Vpp = 0.0 is set for all of them too. And since it works, I guess the problem is not Vpp.

I have no idea which PCMCIA bridge does Toshiba T1950CT use. Since it has no PCI, I guess the PCMCIA bus is mapped to the ISA bus. And then I guess it won't be able to use any 32-bits transfers. Any idea, how to tell cardware/pcdisk/tcm to use 16-bit transfers?

atar wrote on 2026-01-07, 10:27:

douglar wrote on 2026-01-07, 00:05:

Or do you have a read CF that you can test with to verify that the adapter works at all?

Hey, nice avatar. I use dosboot to boot NetBSD 😀. Do you mean to test it in 486 (because it works in i686, as in the original post)? Unfortunately I don't have any CF-cards and this is the question: are there any which support different voltages? And FWIW support different bus modes (16 bits vs. 32)?

Thanks!

Yes, it would be nice to test the 486 with a true CF if that was an option.

My experience is that most CompactFlash devices work at 5v and 3.3v, as dictated by the CF specification.

I hear that some of the really early CF devices and IBM micro drives performed better at 5v than at 3.3v.

The only device that I've ever run across that only worked at 3.3V looked like this--

atar wrote on 2026-01-06, 17:05:

Have anyone managed to read/write SD cards via CF/PCMCIA adapter on PCI-less 486 machines?

I tried this just for fun a long time ago. I have 16, 32, 256 mb SD cards and a 2gig one, I tried them in SD-CF-PCMCIA adapters on a 486 in DOS. Don't remember all the details, sometimes it worked, but mostly didn't. My conclusion overall was that it's not a workable solution.

douglar wrote on 2026-01-07, 13:16:

The only device that I've ever run across that only worked at 3.3V looked like this--

The attachment Untitled.png is no longer available

Looks exactly like my device.

Bondi wrote on 2026-01-07, 13:34:

I tried this just for fun a long time ago. I have 16, 32, 256 mb SD cards and a 2gig one, I tried them in SD-CF-PCMCIA adapters on a 486 in DOS. Don't remember all the details, sometimes it worked, but mostly didn't. My conclusion overall was that it's not a workable solution.

Good to know, thanks! For me it would be enough if I had a single working card. 😀 Do you remember which SD-CF adapter have you used? And have you tried any real CF cards?

atar wrote on 2026-01-07, 15:29:

Bondi wrote on 2026-01-07, 13:34:

I tried this just for fun a long time ago. I have 16, 32, 256 mb SD cards and a 2gig one, I tried them in SD-CF-PCMCIA adapters on a 486 in DOS. Don't remember all the details, sometimes it worked, but mostly didn't. My conclusion overall was that it's not a workable solution.

Good to know, thanks! For me it would be enough if I had a single working card. 😀 Do you remember which SD-CF adapter have you used? And have you tried any real CF cards?

I used the one like shown above, the red one, but mine also said SD/XC on it in the left upper corner.
As for real CF cards, sure, almost all of them work fine in DOS, as long as they are 2gigs or less.

Bondi wrote on 2026-01-07, 16:26:

As for real CF cards, sure, almost all of them work fine in DOS, as long as they are 2gigs or less.

Oh, wow, so my problem is SD-CF? The pure CF cards work with PCMCIA on pre PCI-laptops? Do you remember which PCMCIA manager did you use?

atar wrote on 2026-01-07, 16:43:

Bondi wrote on 2026-01-07, 16:26:

As for real CF cards, sure, almost all of them work fine in DOS, as long as they are 2gigs or less.

Oh, wow, so my problem is SD-CF? The pure CF cards work with PCMCIA on pre PCI-laptops? Do you remember which PCMCIA manager did you use?

I usually use IBM pcmcia drivers, which are default for Thinkpads. But Phoenix and Cardsoft work as well.
And, yes, pure cf cards+pcmcia adapter is actually the prefereed way to transfer files for many people 😀