TPDD: Difference between revisions
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Revision as of 05:18, 31 July 2021
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
Tandy Portable Disk Drive 2
200K, in the form of 2 100K banks
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
- 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.
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)
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.
