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.

Documentation

Tandy Portable Disk Drive

100K

Operation Manual

Software Manual

TPDD1 bootstrap procedure

Command Reference

TS-DOS Directories

Tandy Portable Disk Drive 2

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

TPDD2 bootstrap procedure

TPDD2 Operation Manual

TPDD2 Sector Access

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

KiCAD source: https://github.com/bkw777/TPDD_Cable

PCB: <a href="https://oshpark.com/shared_projects/fr0VwjDP"><img src="https://oshpark.com/packs/media/images/badge-84bb0776ea53b1f532c02df323a90c88.png" alt="Order from OSH Park"></img></a>

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

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

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.