TPDD

Overview

There were two versions of the Tandy Portable Disk Drive. Both were very similar. The drive is a a re-branded Brother FB-100.

Common features of both versions

Size, shape, weight

Batteris: 4 x AA

Wall power: 5.5mm x 2.1mm, 6vdc, center negative, 400ma (Tandy 26-3804)

Media: 3.5" DD, aka "720K" diskettes (not HD 1.44M)

Drive is single-sided. The disks may be single or double-sided, but the drive only uses one side.

Tandy Portable Disk Drive

100K

TPDD bootstrap procedure

TPDD Operation Manual

Command Reference

Software Manual

Tandy Portable Disk Drive 2

200K in the form of 2 100K banks (still only uses one side of the disk)

TPDD-2 bootstrap procedure

TPDD-2 Operation Manual

Parts

Belt

Standard size code: FRW-8.5

Search "FRW 8.5 belt" on Google or ebay

Cable

The "RS-232" interface to the TPDD is actually 0v to -5v TTL, while rs232 serial ports use -12v to +12v. So the cable isn't just a cable, it has electronics to convert the signal levels between TTL and RS232.

Pinout

+------------------------------------------------+
|                                                |
|                                                |
|                 RS-232C                        |
|                   ___                          |
|               +--+   +--+              +-----+ |     
|               | 7 5 3 1 |              | (o) | |
|               | 8 6 4 2 |              |     | |
|               +---------+              +-----+ |
+------------------------------------------------+

1 GND

2 CTS

3 DTR

4 RTS

5 DSR

6 TXD

7 RXD

8 NC

In the beginning, there was the Marty Goodman Document, and it was good.

More recently, Rick Shear has taken a new and very careful look at a real cable, and the Marty Goodman doc, and has probably identified the "mystery" components that Marty Goodman talks about. It looks right, and this cable does indeed work.

Rick's Initial post

Rick's Follow-up

To build a cable based on Rick's pcb, but using all standard parts that you can buy instead of having to find a FB100 cable and destroy it to get the special plug for the TPDD:

Rick's PCB

Components

• The numbers 1-7 on the PCB correspond to the numbers on the TPDD connector in the diagram above. Pin 8 on the TPDD is not used.
• You need a special crimp tool to crimp 28awg dupont style pins. Example: SN-28B Crimp Tool.
• Additional materials:

3/16" heat shrink tubing

1/2" heat shrink tubing (double wall, 3:1 ratio)

• The pins on the db25 connector above will be too long for the solder pads on the pcb. You will need to cut them appoximately in half. Rick used a connector with solder cups instead of through-hole pins, because the solder cup style is what typically comes with typical back shells. But a standard 1.6mm thick pcb doesn't actually fit in betwen the rows of solder cups.
• The back shell is special. Most back shells don't fit in the opening in a Model 100. The back shell in the digikey cart above does.

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Cable BKW 1

Same as above, but the pcb is smaller to allow more room inside the back shell for strain-relief, and the db25 solder pads are longer to fit the pins without cutting.

• Circuit Board

Same components, materials, tools as above

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Cable BKW 4

New design with the transistors on the TPDD end instead of the DB25 end. This way you do not need to crimp Dupont style pins. You just assemble the pcb, cut the 9-pin plug off of a cheap pre-made 9/25 modem cable, and solder the cable with factory molded 25 pin plug to the pcb, and finally secure with some hot-glue, zip-tie, & heat-shrink.

PCB: https://oshpark.com/shared_projects/dyMZxoye

BOM: https://www.digikey.com/short/pbc3pp

Assembly:

• Solder all components to pcb per the render pics.
• Cut the db9 plug off the serial cable. Strip the outer sheath back 1 to 2 inches. Strip each wire 1/8".
• Put 2 to 3 inches of 1/2" diameter heat shrink on the serial cable. (don't shrink yet)
• Use a dmm continuity tester to identify which wires go to which pins on the db25. Find pin 2 on the db25, find which wire goes to pin 2, solder that wire to the hole labeled 2 on the pcb. Repeat for all the numbered holes. Cut any left-over wires short at the cable sheath.
• Secure the end of the cable to the pcb with a zip-tie. Even better, put some glue on the pcb before pressing the cable in place
• Add some hot-glue around the soldered wires where they meet the pcb.
• Pull the two un-soldered pins from the back of the female 2x3 pin socket. Or cut them off with flush cutters.
• Slide the heat-shrink up over the pcb and shrink.

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Software

For PCs

TPDD used double density 3.5" disks, but used a format that is incompatible with modern pc drive controllers. Normal MS-DOS formatted disks are written with MFM encoding, while the TPDD used FM encoding. Even using special software to read non-standard formats, you can't make a normal drive & drive controller read or write FM.

To read or write a TPDD disk from a modern machine, you need a working TPDD drive and the special RS232-to-TTL level-shifting serial cable that came with it, and a "TPDD Client" software to talk to the drive over the serial connection the same way the M100 does.

There are several TPDD clients for more modern machines. Most of these are themselves also no longer modern. For example Lap-Desk and PDD are both 16-bit DOS programs that don't work on Windows.

TpddTool Python TPDD Client

There are several TPDD_servers, which are programs that run on a host pc, that don't *use* a TPDD, but they emulate *being* a TPDD, so a Model 100, 102, 200, WP-2, NEC PC-8201, PC-8201a, PC-8300, Kyotronic KC-85, Olivetti M-10, can save and retieve files on a modern computer.

For M100/102/200

The normal way to use a TPDD is to install a "dos" or TPDD_client on an M100. Several such dos's have been made. The drive came with a utility disk and a functional dos called "floppy". Others have been made by 3rd parties that provided more features or smaller ram footprint or more flexible installation/usage. There are also various special purpose utility programs aside from dos's.