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

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-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)

KiCAD source for schematic & pcb to build a cable

The only difference between these 3 versions of the PCB is the silkscreen.
Each version has the through holes for soldering the wires labelled with numbers for that cable's type of plug and pinout.
The components and traces and signals are identical on the PCBs.

The only difference between the BOM links is the plugs on the included serial cable.
The standard cable (for TRS-80 Model 100 and all other "Model T"s) requires a cable with a 25-pin female plug on one end, and the other end doesn't matter.
The Z88 requires a 9-pin male plug.
The WP-2 and most PC's requires a 9-pin female plug.

All other components are the same.

For use with any "Model T"	For use with TANDY WP-2 and most PC's	For use with Cambridge Z88
PCB	PCB	PCB
BOM (black cable)	Any of the other BOM links will work for this. They all include a cable with a DE9F on one end.	BOM (black 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

For "Model T"s

The normal way to use a TPDD is to install a TPDD_client on a "Model T" such as TRS-80 Model 100 or NEC PC-8201a.

Several such clients 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.
Various special purpose utility programs have been written by users as well.

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, although most of these are themselves also no longer modern.
For example Lap-Desk and PDD.exe are both 16-bit DOS programs that don't work on Windows.

One thing that is usable today is TpddTool.py, a TPDD Client written in Python.

Others

The TANDY WP-2 has support for using a TPDD built in to it's firmware.

There are TPDD Client apps for Cambridge Z88 to use a TPDD.

Related

There are also several TPDD_Emulators, which are programs 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, Cambridge Z88, can save and retieve files on a modern computer using the TPDD protocol.

There are also a few hardware devices that emulate a TPDD.
One was called a NADSBOX, which is no longer available.
Another is a combination of 3 diy projects:
http://github.com/bkw777/PDDuino
http://github.com/bkw777/MounT
http://github.com/bkw777/BCR_Breakout