Looking from advice on a Tandy 1000 SX project

[chrinFinity]

Hi boys

I am so grateful I found this forum, as so far I've not had much luck getting clear answers.

I recently rescued my childhood Tandy 1000SX from the basement of my dad's house, and I'm working on restoring and upgrading it. I could really use some advice from those more in-the-know than myself.

The unit is a standard SX, it has the 640k upgrade, and it has 2 5.25 inch drives which, so far as I can tell, are 360k's. The machine boots perfectly well on MS-DOS 3.3 (the only boot disk i had handy, sadly), so I know its working. Mind you, since it's DOS 3.3 I'm not sure if those disk drives are really 360k, I seem to recall reading somewhere they might have higher capacity if I try to read them on DOS 3.2, but I have no idea if that's true.

There are a lot of things I wish to do with this machine, and I look forward to sharing the experience with all of you, but first and foremost, I really want to get a 3.5 inch diskette drive installed.

In my posession are a couple of 1.44's, tested working. I've done a lot of reading online and I am getting conflicting information from the documentation I've found. Everyone agrees the original Tandy BIOS and motherboard are not capable of accessing 1.44MB disks. Fair enough. But here is where my information gets murky... Some sources are telling me that the SX won't even recognize the existence of a 1.44 drive, that only 720s will do. Yet, other sources are telling me if I put in 1.44's they'll just behave like 720's. Which is correct?

So far I have tried testing each of the 2 drives individually, with and without twisted cable. I did not bother to try both drives together. Should I?

Please note that in the tests I've run so far, I am powering these 3.5's via an AT power supply I've got plugged-in along side the Tandy, as the SX only has 2 molex and I don't have any adapters to plug in the 4-pin 3.5 floppy power directly to the Tandy. I figured I'd cross that bridge if and when I got it working. I am certain the drive is getting power, because I have accidentally connected the floppy cable backwards once or twice, causing the drive to light up and make noise (oops).

So, my new friends, what will it be? Is there something I've not tried, will I have to shell out for exhorbitantly overpriced 720's, or keep my eyes peeled for an ISA floppy controller with its own BIOS which will run the 1.44's at full capacity?

Ultimately my plan is to get one of those floppy-emulators that run off a USB flash drive - 100 floppy images on one usb stick. I don't want to shell out unless I know it's going to work.

Any advice is deeply appreciated. And this won't be my last question. But you all seem so friendly and knowledgeable, I'm looking forward to this forum.

Sincerely,

Christin

 

[pearce_jj]

I realise this doesn't directly answer your question, but I wondered if an XT-IDE and a CF or SD card might be an answer.

Does the SX have DOS in ROM?

 

[deathshadow]

In 3.5" drives the only difference between 720k and 1.44 megs is the sector density -- 9 sectors per track vs. 18 sectors per track. It is for this reason that 720k floppies work just fine in 1.44 meg drives as unlike with 5.25" drives, both are the same number of tracks (80) and use basically the same heads.

Older systems cannot handle the double-data rate eighteen sectors per track uses. (600kbits/sec vs. 300kbits/sec) and so can only use 1.44 meg drives as 720's... so yes, you can use a 1.44 as a 720 in the older systems.

The "problem" is convincing the older machine that it has a larger drive, as most of them (like the tandy EX and SX) will still try to say they only have 40 tracks. Thankfully DOS has the 'driveparm' parameter to let you force the drive type after booting...

But that means you have to boot from a 720k first -- so you should keep the boot disk as 360k... but yes, you could certainly make a 1.44 work as a 720k as the secondary drive by just using the following command in your config.sys

driveparm=/d:1 /f:2 /h:2 /t:80 /s:18

I've got an external 720k on one of my 1000EX that works once that is run.

BUT -- there is one other shortcoming you have to work around. Tandy's use a straight cable, so unless you switch to a twisted cable you have to use a drive that includes a drive-select switch.

Also, don't try it in Tandy's that came with 3.5" drives like the HX -- those carry power on pins that are ground on normal connectors. As you can imagine, plugging a normal 3.5" drive into a Tandy that came with a 3.5" can fail in a most spectacular manner since you're shorting ground to +12 and +5.

As to floppy emulators, avoid the cheap ones that say they're for specific machines, you want one like the HxC. Which gives you full control over the formats.

Interestingly (I'm going to test this when I get one next month) it may be possible to replace all floppies in your SX with one of those as the HxC can emulate two drives of ANY size up to 255 tracks. I'm thinking I might try to get my one of my 1000EX (I have several lesser machines as a spare parts reserve) to boot from a 360k image to get DOS and driveparm in place, to mount a "B" drive that's 255 tracks of 64 sectors per track (at the 300kbit/sec data rate) to give a 16 meg "floppy" image -- the upper limit the DOS 2.2 that's in ROM on the EX can support.

 

[Agent Orange]

ChrinFinity:

1. Go to a computer store and purchase an adapter for your 1.44 drive - about $1.98 or so.
2. If you have and SX then your floppy's are 360 KB.
3. Your would be hard pressed to ever get a 1.2 MB up and running on a SX.
4. The floppys' are jumpered for "A" and "B". "A" normally being on the top. If you choose to install your your 1.44 MB 3.5" floppy in place of the "B" drive no jumpers changes will be necessary.
5. You will need to modify your floppy cable - it won't work with the "twist". I modified mine by carefully cutting out the "twist" and resoldering while using heat shrink tubing for insulation.
6. The system will see the 1.44 as a 720 KB. Note: You must put a piece of tape over the "high density" sensor hole on the 1.44 floppy so it apprears as a 720 KB disk to the system.
7. My SX also has the forum's own XT-IDE hard drive controller kit installed.

If you are serious about your project I will dig out additional info on this. I have previousely documented this same project in the Tandy forum a while back, so you may want to search around the forum.

Good luck!

 

[chrinFinity]

I realise this doesn't directly answer your question, but I wondered if an XT-IDE and a CF or SD card might be an answer.

An XT-IDE with a card adapter might be just what I need, but at present I don't know enough / haven't done enough research to know precisely what to buy or where to get it. My understanding is the range of IDE adapters compatible with the Tandy is limited, and that I have to be able to imitate a particular configuration of hard disk because it's finicky. Do you have more information by any chance?

Does the SX have DOS in ROM?

I think that was an option for the SX. Mine doesn't.

 

[chrinFinity]

But that means you have to boot from a 720k first -- so you should keep the boot disk as 360k... but yes, you could certainly make a 1.44 work as a 720k as the secondary drive by just using the following command in your config.sys

driveparm=/d:1 /f:2 /h:2 /t:80 /s:18

That is very helpful, as a starting point. I believe I will try this solution with one of the old drives booting and the 3.5 as the B: drive. What version of DOS should I try this with?

BUT -- there is one other shortcoming you have to work around. Tandy's use a straight cable, so unless you switch to a twisted cable you have to use a drive that includes a drive-select switch.

So if I can track down a twisted Cable that will connect with the edge connector on the Tandy's 5.25 first, then twists and connects to the 34-pin of the 3.5, that should do it, right?

Also, don't try it in Tandy's that came with 3.5" drives like the HX -- those carry power on pins that are ground on normal connectors. As you can imagine, plugging a normal 3.5" drive into a Tandy that came with a 3.5" can fail in a most spectacular manner since you're shorting ground to +12 and +5.

I have read of this problem and I am grateful I'm working with an SX with 2 5.25's that, my research sources say, is not subject to the power-on-floppy-cable problem.

As to floppy emulators, avoid the cheap ones that say they're for specific machines, you want one like the HxC. Which gives you full control over the formats.

I love the HxC, but it makes me sad that it doesn't come with an attractive form factor. I don't really want a circuit board on wires dangling out the front of my machine

Interestingly (I'm going to test this when I get one next month) it may be possible to replace all floppies in your SX with one of those as the HxC can emulate two drives of ANY size up to 255 tracks. I'm thinking I might try to get my one of my 1000EX (I have several lesser machines as a spare parts reserve) to boot from a 360k image to get DOS and driveparm in place, to mount a "B" drive that's 255 tracks of 64 sectors per track (at the 300kbit/sec data rate) to give a 16 meg "floppy" image -- the upper limit the DOS 2.2 that's in ROM on the EX can support.

That's fascinating - If you post anything about your project I will watch carefully. Thanks for replying

 

[chrinFinity]

1. Go to a computer store and purchase an adapter for your 1.44 drive - about $1.98 or so.

I assume you mean for the power line - I already have it on order. :D

2. If you have and SX then your floppy's are 360 KB.
3. Your would be hard pressed to ever get a 1.2 MB up and running on a SX.

I agree - it looks like the only way would be to find a floppy controller card that has its own bios.

5. You will need to modify your floppy cable - it won't work with the "twist". I modified mine by carefully cutting out the "twist" and resoldering while using heat shrink tubing for insulation.

I am confused - I thought that having the twist nullifies the need for jumpering the "b" drive? Of course the new floppy drives have no jumpers to set, so I was counting on the twist to counteract that. Could you clarify - with the original "A" jumpered 360k as the 'A' drive, and the new 1.44MB drive connected after the twist as the "B" drive, with the modifications recommended to me by deathshadow, should I not have a working B drive behaving like a 720k?

7. My SX also has the forum's own XT-IDE hard drive controller kit installed.

If you are serious about your project I will dig out additional info on this. I have previousely documented this same project in the Tandy forum a while back, so you may want to search around the forum.

Thanks! I'll go looking for it... If you happen to have a link handy that would help too.

Thanks for all your help so far.

 

[deathshadow]

I love the HxC, but it makes me sad that it doesn't come with an attractive form factor. I don't really want a circuit board on wires dangling out the front of my machine

I hear that -- it's also annoying the display it comes with is a hair too large to fit a 3.25" bay AND the form factor of the board doesn't fit a 3.5" bay if you want the card slot facing out.

That's why I was planning to chop a blockoff panel to mount the card slot in the 5.25" bay, while putting the display and buttons elsewhere on the case. I've got a EX here that's missing the tandy badge -- was thinking that would be a neat place to put the display. Thankfully there are spots on the HxC's board to run your own switches to, and the display comes off so you can mount it elsewhere.

Also playing with the idea of just getting the chip for one and building my own board so it actually fits a 3.5" bay. The 1000 HX (which I have two) has bays a fraction taller than a normal 3.5" drive (you put a normal 3.5" in there's like a quarter inch gap at the top), was thinking I could fit the display into one and the buttons and slot the other. Since those also have power on the floppy cable I was hoping to build a custom board that tapped that power instead of requiring a separate connect. (or cutting up a cable to kill the power lines)

Shame it's not "open" for burning your own chips, but the guys who make them do deserve some payment for their efforts.

I've also been looking at their 'track 256' direct access mode to the SD cards. Should be possible to make a driver to mount the SD cards directly... though I've never written a disk device driver... how hard could it be?

A DOS direct driver for the HxC or a similar device would be great for systems that don't have the expansion slots for a hard drive. (PcJr, 1000 EX/HX, some of the old transportables like the sharp PC-7000...)

 

[dabone]

The 1000sx works great with the xt-ide controller.
I'm just going to part mine out, it's too expensive to try to order parts to trouble shoot.
I've got a 720k 3.5" Tandy Drive for the sx for sale. No adapter needed, works on the standard dual drive cable in the sx and has the correct power adapter and mounting adapter.
As far as I can tell this was a tandy option for the 1000 line.

I've also got a 8bit scsi card and cdrom that work well in a sx also.

Later,
dabone

 

[Agent Orange]

An XT-IDE with a card adapter might be just what I need, but at present I don't know enough / haven't done enough research to know precisely what to buy or where to get it. My understanding is the range of IDE adapters compatible with the Tandy is limited, and that I have to be able to imitate a particular configuration of hard disk because it's finicky. Do you have more information by any chance?



I think that was an option for the SX. Mine doesn't.

Virtually any 8-bit ISA card will work in the SX. DOS is not in ROM on the SX. Your SX originally came with MS-DOS 3.3 (Tandy only vers. It's fixed so that it only boot on a Tandy but is otherwise fully compatable). Should be noted that any DOS up through 6.22 boots just fine on the SX. Send a PM on this site to HARGLE and/or LYNCHAJ. They can help you get the materials together, just takes a little bit of solding on Saturday afternoon and you'll be good to go.

 

[chrinFinity]

... (explanation of modification plans) ...

That's impressive. Too ambitious for me! I don't have the tools or the skills. But I wish you luck and I'd love to see the results.

I've got a 720k 3.5" Tandy Drive for the sx for sale. No adapter needed, works on the standard dual drive cable in the sx and has the correct power adapter and mounting adapter.
As far as I can tell this was a tandy option for the 1000 line.

Can you PM me with details? Is that allowed on this forum?

I've also got a 8bit scsi card and cdrom that work well in a sx also.

Could I theoretically run the cdrom and a scsi hard disk from the same card? Would either device be bootable?

Send a PM on this site to HARGLE and/or LYNCHAJ. They can help you get the materials together, just takes a little bit of solding on Saturday afternoon and you'll be good to go.

Is this a realistic project for someone who would be buying her first soldering iron and whose never used one before? If you say "yes," I'm willing to try. I learn quickly.

Thank you all for your guidance.

-=Christin

 

[Agent Orange]

You can handle the soldering. Google the procedure. You can get all the materials that you need as Radio Shack for less than $15.00. You have a whole forum here at your disposal to help you with the project.

P.S. About the twist in the floppy cable: The SX had "straight through" cables because you were able to select "A" or "B" by changing jumpers on the floppy drive. They were preset that way at the factory. The aftermarket 1.44 3.5" inch floppy's are normally hardwired to the "DSO" or "A" position. The "twist" makes the "A" floppy a "B" floppy with out modifing the drive itself.

 

[kb2syd]

P.S. About the twist in the floppy cable: The SX had "straight through" cables because you were able to select "A" or "B" by changing jumpers on the floppy drive. They were preset that way at the factory. The aftermarket 1.44 3.5" inch floppy's are normally hardwired to the "DSO" or "A" position. The "twist" makes the "A" floppy a "B" floppy with out modifing the drive itself.

You got that a little twisted. The floppies today are hard wired as "B" (DS1). The twist in the cable gives you "A" (DS0).

 

[pearce_jj]

Is this a realistic project for someone who would be buying her first soldering iron and whose never used one before? If you say "yes," I'm willing to try. I learn quickly.

Maybe, I would say. Personally I found the XT-IDE boad a bit tricky to solder (some of the joints just wouldn't flow). I got 2 good cards out of 3 (not looked at the disfunctional card in any detail yet). Probably there was some grease on them or similar.

If you are going to give it a go, get a temperature controlled soldering iron an 0.7mm tin-lead multicore solder, and mount all the ICs in sockets (so you don't need to solder the ICs directly). Also required will be a bright desk lamp and some coffee.

Maybe someone on here might make one up for you? I'll offer - but with my track record you may not want to take that up!

 

[Agent Orange]

Well excuse me! Thanks for pointing that out. The point was you do not use a twisted cable on the SX when using a 3.5" floppy. As a matter of fact, I resoldered the jumper on my SX's 3.5" 1.44 MB floppy and it's now the "A" drive.

 

[wondow]

Network?

Network?

I had one of those tandy 1000 SX computers as a teenager. It used to have the 640k upgrade, a 20 mb hard drive card and the 286 express card. Too bad I don't have it anymore, since I miss it a lot. Well, as for your drive problem, you could simply do what I did; to purchase an ISA network card and use the high density drives from another computer. On my 1000 SX, a standard 16 bits ISA plug and play network card worked just fine. I was even able to use it to go on the internet.

Good luck with your project!

 

[IBM Portable PC]

I've been toying with a Tandy 1000 (original version) and 720K boot floppies and it seems to work......most of the time, other times it hangs.

I've also just bought a 720K Gotek FDD emulator for about $45 and I can read the emulated floppy via other systems but cannot boot from the 1000, it reports "insert system disk.......". The activity LED flashes, but it can't read the emulated 720K floppy.

Is DRIVEPRM likely to help DOS boot or is there another issue here I.e. shoud I be able to boot from a 720k disk (real) at all?