I looked at some pictures and most all the TM850 variants w/bios do have that NAND. http://vogonsdrivers.com/getfile.php?fileid=723&menustate=0
https://i.ebayimg.com/images/g/kqYAAOSwHxJkdkuP/s-l1600.jpg , https://forum.vcfed.org/index.php?attachments … 815-jpg.991578/
850MEX w/o bios https://i.ebayimg.com/images/g/bx0AAOSwJstgSVZB/s-l1600.jpg looks like the one on vcfed
Of my five 8-bit scsi cards only 3 have term power jumpers, the other 2 rely on term power from the HD.
added It appears that NAND goes to high address lines or OIW/IOR and DACK/DRQ lines from quick look but hard to tell, could be needed for setting the BIOS starting address or just general read/write stuff....
did not find any MEX with bios...just others

added2: my Laser XT/3 has a scsi card, when the RLL drive died decided to go scsi. A Storage Dimensions DataCannon 801 with 200Mb IBM scsi hd. Works great !
Those old scsi adapters do have limits, think 540MB same as early IDE as my 800MB was seen but caused a bios failure on same controller.

Tnx

Aware that the old adapters have limits, have a 52MB drive I was considering (although there's also a physically massive 5.25" full height 640MB drive that would be amusing if it did work.

My MEX PCB is identical to the first eBay link you gave - https://i.ebayimg.com/images/g/kqYAAOSwHxJkdkuP/s-l1600.jpg -, just minus the EPROM, the LS244 and C2, so that's pretty much what I need then - U1 (the LS00), L1, R2, C1, C6 and C7 are also unpopulated there. That means C2 is the only unknown. I can't make much out from the pic. What I can see on my board is that its left pad connects to pins 27 and 28 on the EPROM (resp Program and Vcc accourding to this datasheet) and its right pad goes to ground - so sounds like a filter cap. The same datasheet states:

It is recommended that a 1μF ceramic
capacitor be used on every device between VCC
and VSS.

So I suspect a 1uF SMD cap is the way to go. Sound likely?

Yes sounds likely. It appears your adapter has permanent Term power (the fuse and diode). You can check the resistor packs, should be a trace from the fuse to one end of each of those packs (if similar to most), with the other end grounded.
A voltmeter should show about 5v off the fuse toward those packs.
Similar but diff: I have a Rancho Tech 1000B that has similar layout and is full scsi, supports two HD and cdroms, etc.
also have a Iomega version of the 1000B that is missing the fuse, internal 50 pin connection and IRQ jumper headers (also it has a limited Iomega BIOS that that requires a driver), was used with a scanner or some such external scsi device.
Would like to someday fix it (the Iomega one) and put the proper BIOS on it for use with HD's but have not had the time.
Keep us updated please !

Shall do - will be ordering the LS244 and some 1uF caps. I already have some 2764-compatible EPROMs (and hopefully 28p sockets) from another project and have found the Future Domain SCSI BIOS v 8.2 (needed for XT and large drive support).

Grest ! I should have mentioned that Term Power also goes to pin 26 of the 50 pin scsi bus connector on many older adapters that have a jumper for it.

Have done something I should have done before opening this topic and tested the card. Fortunately all is good. Did take a lot of digging through partially redundant software and documentation sources. Just in case anyone else stumbles on the topic a few pointers and links (active as of January 2024)

After all this time, Future Domain became Adaptec became Microchip - and still there are drivers for the TMC-850M (and derivatives) on the official website, here to be precise. You'll find "DOS Drivers" and "PowerSCSI version 4.1" there. In fact, the DOS Drivers are all also present in the PowerSCSI version 4.1 download and a lot more useful stuff besides. So take that. It's a compressed self-extracting archive, but not in any format 7Zip can make sense of, so just get it to your old machine and run it there.

If your card has a SCSI BIOS 'it just works' for HDDs, no drivers needed. Without SCSI BIOS you need to load drivers for the card, which turn out to be DCAM950.EXE (despite the apparent model number mismatch, the '950' refers to the controller chip used on the 850 cards, but this isn't mentioned in documentation). Syntax is odd: you give it the base address of the card with a slash (/) followed by the IRQ without a slash, so in my case:

DEVICE=DCAM950.EXE /CA00 5

You then need to load the BIOS with FDBIOS.SYS. This one doesn't need parameters.

For CDRom you normally want to load an ASPI driver for the card and then an ASPI CDRom driver. You can do that - load DCAM950.EXE first with its parameters for your card, then ASPIFCAM.SYS and finally ASPICD.SYS (not included) with your favorite driver name /D:
But Future Domain also provides FDCD.SYS. It doesn't need any other drivers to be loaded for the card, you just feed it your favorite driver name as /D: and it detects the card and any CDRom drives connected automatically. All you need afterwards is MSCDEX.EXE or alternative.

Finally, in the DOSUTILS directory you get the FDSDA .EXE (Future Domain SCSI Device Analyzer), which is a great little tool to see if the adapter is recognized at all and which devices it detects on the SCSI bus, regardless of drivers.

Incidentally, to do all this I needed to get my vintage testbed network back up and running, which was a bigger chore than expected (mainly due to a brand-new good-brand UTP cable being unexpectedly dud despite link LEDs lighting up) but needed doing and now I can share files easily via FTP again.

Anyway, I'm tired but happy, now to order the LS244 and get to bed 😉

Great work! Good explanation. Yeah every controller back then had its uniqueness and learning curve. Seems working with old scsi stuff is becoming a lost art sort of like working with MFM/RLL.
Which BIOS are you going to try first ? From MinusZero it appears you have a choice, think 8.4 would be a good start, if it gives issues fall back to 8.2 ?
Not many around with 8bit scsi adapters anymore, fewer with the less than 1GB scsi hd's.
When you get it all done need to post to Vogons library everything you found for your card.
added: found this in the archives, you probably already have it.... (was a .bmp converted to .jpg):

Horun wrote on 2024-01-06, 02:30:

Great work! Good explanation. Yeah every controller back then had its uniqueness and learning curve. Seems working with old scsi stuff is becoming a lost art sort of like working with MFM/RLL.
Which BIOS are you going to try first ? From MinusZero it appears you have a choice, think 8.4 would be a good start, if it gives issues fall back to 8.2 ?

8.2. It's the last version to work in XT-class computers - which is what I want this card for - and the first with large drive support. Also it's the only one I could fairly easily find.

Not many around with 8bit scsi adapters anymore, fewer with the less than 1GB scsi hd's.

Exactly. I was very happy when this one popped up on Amibay.

When you get it all done need to post to Vogons library everything you found for your card.

Yep, will upload it to Vogonsdrivers.

Won't be much - given that the pwrscsi4.exe gives all the drivers and the diag util, I don't anticipate needing more than that and the BIOS image - and a TXT file with instructions.

Have found all the parts locally, so with a bit of luck I'll receive it all next week.

You may have found this archive of some FD stuff in the past: http://edv-janssen.synology.me/ct_treiber_ser … uture/files.htm
above worked in October 2022 (from my FF history), wayback has one archive but no files: http://web.archive.org/web/20220720203735/htt … uture/files.htm
this one is a mirror with obtainable files: https://ftp.zx.net.nz/pub/archive/ftp.dyu.edu … C/FutureDomain/
added: found this manual for a NEC scsi cdrom, the included controller (XT003FD) is a TMC-850:
http://archive.retro.co.za/archive/computers/ … I-Interface.pdf

Horun wrote on 2024-01-06, 16:19:

You may have found

Found quite a bit more, but it was generally redundant - that PowerSCSI download included a lot.

this archive of some FD stuff in the past: http://edv-janssen.synology.me/ct_treiber_ser … uture/files.htm
above worked in October 2022 (from my FF history), wayback has one archive but no files: http://web.archive.org/web/20220720203735/htt … uture/files.htm

Sadly dead links indeed.

this one is a mirror with obtainable files: https://ftp.zx.net.nz/pub/archive/ftp.dyu.edu … C/FutureDomain/

Tnx, good stuff in there, particularly for non-DOS systems.

added: found this manual for a NEC scsi cdrom, the included controller (XT003FD) is a TMC-850:
http://archive.retro.co.za/archive/computers/ … I-Interface.pdf

Nice extensive documentation - apart from the BIOS, this is 100% relevant to the TMC-850MEX card, in particular the address and IRQ settings.

Yeah and pdf explains a bit on some of the files, the FDBIOS.sys is interesting. Your TMC-850 might support up to 2Gb HD's with it. Did not have time to search when you first posted but was off work today and looked around a bit.
Did see one (850MEX) on ebay for $50 semi-local, might make an offer but will wait to see how your work goes. It need the fuse, LS244, rom socket and C2 from the pictures and maybe a few other parts...
Layout is a bit diff than yours: https://i.ebayimg.com/images/g/T6wAAOSw3GZkpvtW/s-l1600.jpg

Hello
Here are photos of my TMS-850 card if you need them.
The tested one works with a 6.4Gb disk on the XT.
However, I created the (small) partition on another computer with a different SCSI controller - today I don't remember why I did it.

Perfect. Tnx!

That's confirmation I've ordered the correct parts - and that BIOS 8.2 does what I hope it will.

Update:
Two packages arrived so got down to some soldering.

Before:

After:

Unfortunately I have managed to misplaced the termination power fuse, so this is just the LS244, filter cap and socket.

I've confirmed card is still working correctly, now to find those EPROMs...

...and found them -Atmel 28C64B EEPROMs that are still fairly readily available. Flashed the image and this was the result:

Success, it pops up at boot and detects drives. Even VERY big drives like this Quantum Atlas IV 18GB monster. In fdisk it only shows 1292MB so something not right. Why am I testing with such a huge drive? My ex-Sun ST31200WC (1.2GB and noise to rival a 747 going to full thrust) doesn't spin up. Not sure if it's controller, drive or SCA-50p adapter related, but one way or another not working. And my 640MB drive is holding up the monitors on my son's desk (er, srsly) and I can't find that old 50MB disk.

So can't test end-to-end yet, but looks like the operation has been completely successful 😀

Will try to extract usable drive from that desk and confirm 100% asap.

Update: complete success 😀

Booting onto a Turbo XT board with a 767MB monster of a full-height 5.25" SCSI drive.

Running PC-DOS 7 2000 as the most lightweight DOS (RAM footprint) to support>32MB partitions.

I'll edit the topicstart with full Howto and upload the necessary files to vogonsdrivers.com - done!