TPDD

Tandy Portable Disk Drive

There were two versions of the Tandy Portable Disk Drive, "26-3808 Tandy Portable Disk Drive" or "TPDD1", and "26-3814 Tandy Portable Disk Drive 2" or "TPDD2". Both were very similar. The original TPDD1 is 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.

Documentation

Tandy Portable Disk Drive

100K

Operation Manual

Software Manual

Service Manual

TPDD1 bootstrap procedure

Command Reference

Tandy Portable Disk Drive 2

200K, in the form of 2 100K banks

TPDD2 Operation Manual

TPDD2 bootstrap procedure

TPDD2 Sector Access

Parts

Belt

Standard size code: FRW-8.5

Search "FRW 8.5 belt" on Google or ebay

Cable

The "RS-232C" interface to the TPDD is actually 5v TTL (0v to +5v), while RS-232 serial ports use -12v to +12v. So the cable isn't just a cable, it has electronics inside the DB25 plug to convert the signal levels between TTL and RS-232.

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 EB+ (External Battery +4.8 to +6v) (Only on TPDD2, n/c on TPDD1)

KiCAD source for schematic & pcb to build a cable

Assembly:

• Solder all components to pcb per the render pics.
• Pull the two un-soldered pins from the top of the socket and discard.
• Cut the 9-pin 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)
• Identify which color wires go to which pins on the DB25 plug.

Find pin 2 on the db25

Find which color wire goes to pin 2 using a DMM continuity tester

Repeat for all the numbered holes on the PCB: 2,3,4,5,6,7,20

Cut any left-over wires short right at the cable sheath.

• Solder the wires to their matching numbered holes, with the wires on the top side (without the transistors).
• Put some hot-glue on the top side of the pcb in the "dog bone", press the end of the cable into the glue, and secure to the pcb with a zip-tie.
• Add some hot-glue around the soldered wires where they meet the pcb to immobilize them.
• Slide the heat-shrink up over the pcb and shrink.

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TPDD:Other_Cable_Designs

Software

Software related to these drives can be broken into 2 main categories, clients and servers.

A TPDD client (aka DOS) is software that uses a TPDD drive. This includes the "Floppy" that came on the utility disk that came with the drive, TS-DOS, and others.

A TPDD server (aka emulator) is software that pretends to BE a TPDD drive. This includes LaddieAlpha, dlplus, and others.

Misc Related Info

TS-DOS implements an extension to the TPDD protocol to provide subdirectories.
A real TPDD or TPDD2 doesn't support this, but some TPDD emulators do (NADSBOX, PDDuino, LaddiAlpha at least)

TS-DOS Directories

TPDD uses standard 720k DD 3.5" disks, but uses a format that is incompatible with modern pc drive controllers.
Normal MS-DOS formatted disks are written with MFM encoding, while the TPDD uses FM encoding.
Even using special software like TeleDisk to read non-standard track/sector formats, you can't make a normal drive & drive controller read or write FM. An old pc with an early floppy controller chip and an old 720k drive may be able to do it.

To read or write a TPDD disk from a modern machine, you need a working TPDD drive, the special RS232-to-TTL level-shifting serial cable, and "TPDD Client" software to talk to the drive over the serial connection the same way the M100 does. See PDD.EXE or TpddTool.py from the TPDD clients link above.

Don't use 1.44M HD disks in a TPDD. Use 720K DD disks.