The Epson TF-20

Front Epson Flexible Disk Drive Unit TF-20 The TF-20, with the HX-20 option installed, brought floppy disks to the HX-20 machine. The disk drives are the same as the QX-10 devices, and even the disk format is identical. Note however that the drives type is SD-320, which is a SD-321 (as in the QX-10) but with a Head load selenoid. Here a movie of the head positioning voice coil. The floppy and the head are on the left.
The TF-20 is a peculiar device in that it contains a complete computer system that boots from the disk. It is Z80 based, has 64 kByte RAM (not a trival amount in 1982!), a boot PROM, serial interface and floppy controller (µPD765A). Once the OS, 'TFDOS' is loaded, it can communicate to external devices like the HX-20 or PX-8. There is no console connection to check booting has succeeded, but if the drive A is repeatedly accessed, assume booting has failed. A succesful boot accesses the disk exactly three times, where there is a short pause between the first and second time. Hard to explain in words, so I made a movie.
The TF-15 looks very similar, but has less RAM (2 kByte) and the OS in ROM (8 kByte). Only the PX-4 and PX-8 commands are supported, not the HX-20 commands. (TSD881a)

Back Epson TF-20 backside The basic TF-20 contained just two floppy drives and a power supply. With the flat cable connector, the unit could be used as extra drives with a QX-10. Only with the HX-20 factory option installed, it became an intelligent disk station to be used with the HX-20 and later the PX-8 and PX-4.
Some specs:
Serial interface baud rate: 38400 bd
40 track double density, 16 sectors of 256 bytes per track/side. The disk geometry is identical to that of the QX-10, so the first four tracks are reserved for CP/M CCP, BDOS and a large BIOS. Track 4 is the directory and track 39 is not used. This leaves 278 kByte per disk for use data. A system disk, containing BOOT80.SYS (TF-20 boot file, also referred to as TFDOS) and DBASIC.SYS (HX-20 Disk basic extension) has about 8 kByte less space.
An image is available.
The manual and schema are available from the documentation directory

Connectable
to TF-20 with PX-8 & HX-20 The TF-20 works equally well with the HX-20 as with the PX-8 as both share the same baudrate and serial protocol. The commands used however differ; the HX-20 retrieves and stores files, the PX-4/8 operates on sector level.
For connection with the HX20 you need Cable #707. For the PX-8 use cable #723.

Comparable
devices comparable diskdrives The TF-20 is in functionality comparable with the Commodore 1541 disk drive. Local intelligence and a serial interface with the host system. The Sharp drive looks similar but lacks most logic: it only has a floppy controller on board, and is a parallel I/O device for the host computer.

Local links:

Boot ROM
HX-20 page
PX-8 page
PF-10, the portable successor.
HX-20 boot disk image Contains TF-20 boot code and HX-20 Disk Basic extension.
Epson Serial Protocol used between TF-20 and HX-20, PX-8, PX-4.
More on EPSP
Fixing diskette load and eject issues
Booting TF-20
head positioning voice coil
Scanned documentation in PDF
The PX-8 disk utilities
PFDBK, the Arduino based simulator

Last update: 2023-08-17

fjkraan@electrickery.nl

Front		The TF-20, with the HX-20 option installed, brought floppy disks to the HX-20 machine. The disk drives are the same as the QX-10 devices, and even the disk format is identical. Note however that the drives type is SD-320, which is a SD-321 (as in the QX-10) but with a Head load selenoid. Here a movie of the head positioning voice coil. The floppy and the head are on the left. The TF-20 is a peculiar device in that it contains a complete computer system that boots from the disk. It is Z80 based, has 64 kByte RAM (not a trival amount in 1982!), a boot PROM, serial interface and floppy controller (µPD765A). Once the OS, 'TFDOS' is loaded, it can communicate to external devices like the HX-20 or PX-8. There is no console connection to check booting has succeeded, but if the drive A is repeatedly accessed, assume booting has failed. A succesful boot accesses the disk exactly three times, where there is a short pause between the first and second time. Hard to explain in words, so I made a movie. The TF-15 looks very similar, but has less RAM (2 kByte) and the OS in ROM (8 kByte). Only the PX-4 and PX-8 commands are supported, not the HX-20 commands. (TSD881a)
Back		The basic TF-20 contained just two floppy drives and a power supply. With the flat cable connector, the unit could be used as extra drives with a QX-10. Only with the HX-20 factory option installed, it became an intelligent disk station to be used with the HX-20 and later the PX-8 and PX-4. Some specs: Serial interface baud rate: 38400 bd 40 track double density, 16 sectors of 256 bytes per track/side. The disk geometry is identical to that of the QX-10, so the first four tracks are reserved for CP/M CCP, BDOS and a large BIOS. Track 4 is the directory and track 39 is not used. This leaves 278 kByte per disk for use data. A system disk, containing BOOT80.SYS (TF-20 boot file, also referred to as TFDOS) and DBASIC.SYS (HX-20 Disk basic extension) has about 8 kByte less space. An image is available. The manual and schema are available from the documentation directory
Connectable to		The TF-20 works equally well with the HX-20 as with the PX-8 as both share the same baudrate and serial protocol. The commands used however differ; the HX-20 retrieves and stores files, the PX-4/8 operates on sector level. For connection with the HX20 you need Cable #707. For the PX-8 use cable #723.
Comparable devices		The TF-20 is in functionality comparable with the Commodore 1541 disk drive. Local intelligence and a serial interface with the host system. The Sharp drive looks similar but lacks most logic: it only has a floppy controller on board, and is a parallel I/O device for the host computer.