TEAC FD-55GFR and the Model 1

[LambdaMikel]

Well, I knew it wasn't going to be easy, but I had to try - given the availabilty of NOS TEAC TD-55GFRs on Ebay. So I got one. Some sites (e.g., Tim Mann's TRS-80 pages) also suggest that this is a viable option. Others say they had no success with that drive at all.

I know that these are 1.2 MB, and I also figured out how to jumper them to 300 RPM.
However, I am still - at best - getting a "DISK ERROR", at worst just a blank screen (depending on the jumper settings).

I have disconnected the HD selection pin and soldered it to GND and then set the DUAL MODE / LG / I jumpers so that a low / GND on Pin 2 would force 300 RPM regardless. And that also seems to work. I also jumpered RDY instead of DC. I also tried all combinations for the remaining jumpers (E2, IU), but no success.

Well, I actually tried one of my standard 40 track SSDD disks that work in my other drive. Is it possible that I really need HD media, and maybe rewrite the disks? The DISK ERROR message is at least somewhat encouraging. I can also see the head move, so something is working.

Anybody managed to get that drive working on the Model 1? Please share how. Thanks!

https://deramp.com/downloads/floppy_drives/teac/TEAC FD-55GFR.pdf
https://retrocmp.de/fdd/teac/TEAC_FD-55_Jumper-settings.pdf

 

[ldkraemer]

Here is a PDF with the few pages for the TRS-80 Model 1 (Modified from my Model 3 & 4 Document) that shows
how I interfaced my Model 4 to a 3.5" External Floppy Drive.

Note: You will ONLY have Single Sided Floppy's, and unless you have a FDC Doubler, you will just have SD not DD.
Also Pin 32 is /NDS4 (DS3) = DS{0..3}, and not Side Select.

So, if you print out page 3, then mark up anything you find that needs to be strapped (HIGH or LOW) to satisfy
the Teac FD-55GFR, you should be able to get it to read a 360K Density 40 Track Drive. The problem is I don't
think there is a Double Step Rate available to step the Teac two tracks for each track stepped by the FDC.
At least right now I don't remember any easy way to get two steps per track. If you are using NEWDOS 80
there might be a PDRIVE setting that allows double stepping. I'd have to dig through the manual.

Be sure to double check Pins 10, 12, 14, 32, and 16 as I quickly edited my document. I could have made a mistake.
Then for the Teac Drive on the Right (last page), double check the signals that do not connect to the FDC, so they
are strapped (or PULLED UP correctly) to satisfy the Teac settings as per the TEAC Manual.

If you want the .DOC file or my Model 3 & 4 Doc, PM me.

Larry


View attachment Model1_35_Drives.pdf

 

[lafos]

Did you try to format a blank disk? The Teac FD-55GFR will be seen as an 80-track drive so a standard 40-track disk will not read properly. Most TRS-80 DOSs allow for 80-track drives, either single or double sided (except TRSDOS, of course). You will not be able to easily swap media between the 80 and 40 track drives.

DOSPLUS 3.5 does have a SKIP parameter for double stepping a floppy drive. See Library command CONFIG on page 2-34 of the DOSPLUS manual.

MultiDOS latest version also has a skip function in the CONFIG command. I suspect that LDOS and NewDOS80 do as well.

I have used 3.5" drives in my Model I as DSDD (double sided double density) 80-track drives. If you have the hardware jumpers set up, then it should work with the limitations about tracks.

 

[ldkraemer]

Yes, NewDOS 80 for the Model 1 has the PDRIVE command that allows selecting the type Interface and
the type of Floppy Drive(s).

TD is the Type of Drive specification. The definitions are:

1. TD=A 5 inch, single density, single sided drive

2. TD=B 8 inch, single density, single-sided drive

3. TD=C 5 inch, single density, double sided drive

TD=C


TI=type1 specifies the type of disk drive interface. type1 consists of one or more alphabetic letter flags chosen from the list below.
For the Model I, one and only one of flags A, B, C or E must be chosen. For the Model III, one and only one of flags A or D must be
chosen. The other flags are optional depending upon the interface. Certain flags are inter-drive mutually exclusive meaning that
for a given drive dn1, if one dn2 drive specifies a flag that is inter drive mutually exclusive with another flag, then another dn2 drive
may not specify the excluded flag. For now, flags B, C and E are interdrive mutually exclusive for the Model I.

Flag A means the standard disk interface is to be used for diskette I/O for this drive. For the Model I this interface supports drive
 types A and C. For the Model III this interface supports drive types A, C, E and G.

Flag B (Model I only) means that an OMNIKRON mapped type interface is installed and is to be used for I/O for this drive. This interface
supports drive types A, B, C and D.

Flag C (Model I only) means that a PERCOM doubler type interface is installed and is to be used for I/O for this drive. This interface
supports drive types A, C, E and G.

Flag E (Model I only) means that an LNW type interface is installed and is to be used for I/O for this drive. This interface supports
drive types A through H.


Flag L means two step pulses between tracks. This allows a 35 or 40 track diskette to be read on an 80 track drive. Writing can also be
done in this manner, but the 35 or 40 track drives have trouble reading some of the sectors so writing is not recommended.

TI=AL

It should work fine for NewDOS 80, assuming your PDRIVE settings are correct.


Larry

 

[LambdaMikel]

Thanks guys, that is very helpful!

I wasn't aware that 40 track disks would not read with TRSDOS. So,


"Flag L means two step pulses between tracks. This allows a 35 or 40 track diskette to be read on an 80 track drive. Writing can also be
done in this manner, but the 35 or 40 track drives have trouble reading some of the sectors so writing is not recommended."

That doesn't sound too positive though.

Would you reommend getting the PERCOM doubler?
https://www.ebay.com/itm/Double-Den...663296?hash=item23cd169000:g:0UsAAOSwGPxaJ7Mz

OK, I will try if I can already format with NEWDOS/80. I must say that all the different OSes still present a bit of a mystery to me (especially since I have very little documentation.

Would that be a good NEWDOS/80 manual?
https://www.classic-computers.org.nz/system-80/software-manuals/manuals-NewDOS-80_v2.0_manual.pdf

My default OS for the Model 1 is LDOS (5.3.1), so ideally I would want to have the drives working with that (with 80 tracks then). Just found the LDOS manual and reading about the different disk format (it can do 80 tracks, but I do not see the double stepping option in the SYSTEM command).

https://www.tim-mann.org/trs80/doc/LDOS & LS-DOS Reference Manual M-40-060 (1992).pdf

Anyhow, 80 tracks should be fine too.

 

[Chuck(G)]

Don't know much about the Model I, but isn't that an 8" drive system? Given that 8" drives are 360 RPM/77 tracks, why would one want to jumper the drive to do 300 RPM? A 1.2M 5.25" drive is very close in specs to a regular 8" drive.

Call me curious.

 

[Eudimorphodon]

Don't know much about the Model I, but isn't that an 8" drive system?

Nope. That’s the Model II. Model I’s original drive format was 35 track single density 5.25”.

 

[Chuck(G)]

Nope. That’s the Model II. Model I’s original drive format was 35 track single density 5.25”.

Okay, I remember that Model I used a 1771 for the disk drive controller, which I normally think of as an 8" controller (cf datasheet). That's what probably caused the brain fart. So, what, <90KB on a 5.25" 48 tpi SSSD floppy? Rig up an MCU interfacing with a 32GB SDHC card and you could probably store all the software for the Model I ever written--and still have room left over...

 

[LambdaMikel]

Okay, I remember that Model I used a 1771 for the disk drive controller, which I normally think of as an 8" controller (cf datasheet). That's what probably caused the brain fart. So, what, <90KB on a 5.25" 48 tpi SSSD floppy? Rig up an MCU interfacing with a 32GB SDHC card and you could probably store all the software for the Model I ever written--and still have room left over...

Yeah, if have FreHD and HxC and a real 48 tpi SSSD floppy for my Model 1. That's not the problem

*Real* floppy drives are cool So I want them - more retro! I wouldn't want to jump through the 8" hoop though. Too much trouble getting media and servicing them.

Also - the kids are intruiged by them! By now they know that there once was a time where *the phone was connected with a wire to the wall* (can you imagine?), and there were vinyl records. To them, the 5.25" disks are as intruiguing as clay tablets.

 

[Eudimorphodon]

So, what, <90KB on a 5.25" 48 tpi SSSD floppy? Rig up an MCU interfacing with a 32GB SDHC card and you could probably store all the software for the Model I ever written--and still have room left over...

Even a plain 720k floppy (assuming you can lay hands on a double density board) is basically like having a hard disk on those things, yeah.

 

[Chuck(G)]

Weren't there DSDD retrofit kits for those?

ISTR that early TRS-DOS used address marks with the 1771 that later WD controllers couldn't uniquely distinguish from others when reading. I believe there were patches to get the thing to work with the 1791 controllers.

 

[LambdaMikel]

Success! These drives work as 80track drives!

What's more, it doesn't even need hardware mods! I have a non-standard FDC cable though (I don't have the TRS Drive Select CutOuts etc. and jumper the drives for DSx).

The jumper settings that work (with my cable, but that shouldn't make a different) are shown in the pic:




Weird - it also works with DC instead of RDY jumper. Maybe Newdos doesn't care??

OK, so much for the lunch break - back to work...

Thanks again for the help!

PS There are still some NOS of these on Ebay.... they are not cheap, but seems they are a good addition to the TRS-80.

 

[Eudimorphodon]

Weren't there DSDD retrofit kits for those?

ISTR that early TRS-DOS used address marks with the 1771 that later WD controllers couldn't uniquely distinguish from others when reading. I believe there were patches to get the thing to work with the 1791 controllers.

Most (all?) TRS-80 Model I double density boards piggybacked into the 1771 socket and had spots for *two* controller chips in parallel, the original 1771 which was moved to it and a 1791 or equivalent. A latch selected which chip was active, and on reset the 1771 was in charge so backwards compatibility with unmodified TRS-DOS could still be a thing. (I don’t actually know off the top of my head if TRS-80 DOSes that supported DD cards used the single density talents of the 1791 when doing mixed density operations like writing single density boot tracks on otherwise double density disks, or if they just switched controllers.)

 

[lafos]

Most (all?) TRS-80 Model I double density boards piggybacked into the 1771 socket and had spots for *two* controller chips in parallel, the original 1771 which was moved to it and a 1791 or equivalent. A latch selected which chip was active, and on reset the 1771 was in charge so backwards compatibility with unmodified TRS-DOS could still be a thing. (I don’t actually know off the top of my head if TRS-80 DOSes that supported DD cards used the single density talents of the 1791 when doing mixed density operations like writing single density boot tracks on otherwise double density disks, or if they just switched controllers.)

TRSDOS used nonstandard DAMs for the directory, which the 1791 could not distinguish. All other DOSs, especially once DD was supported, could work fine with the 1791, as they used the standard DAMs. MultiDOS was unique in offering a DDAM/CMD file which could convert DAMs for TRSDOS and NewDOS+ to the other format.

From the MultiDOS manual published in 2010 by Vernon Hester:

MODEL I
DDAM Change address marks on a single density diskette’s directory.
DDAM[ [:]d] (param)
d = logical drive number
param = U for USER DEFINED: used by TRSDOS® 2.3 and NEWDOS/21 on the Model I.
param = D for DELETED: used by all double density systems, MULTIDOS and LDOS on the Model I.

 

[LambdaMikel]

The double stepping also works! Using a

PDRIVE,0,2,TI=AL,TD=A,TC=40,SPT=10,TST=3,GPL=2,DDSL=17,DDGA=2

I can read my 40track disks (in drive 2). Nice! NewDOS is neat! One can learn a lot about floppy drives from it (and from you guys of course )

Put the 2 new TEACs in an old SCSI enclosure, as drives 1 and 2. I am booting from the HxC, drive 0. Maybe I put in a drive selector at some point.