The Epson TF-20

Front Epson Flexible Disk Drive Unit TF-20 The TF-20 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.
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 is loaded, it can communicate to external devices like the HX-20 or PX-8.
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 flat cable connector is not used when the unit is configured as a HX-20 disk drive unit. There probably was another configuration like extra disk drives for a QX-10.
Some specs:
Serial interface baud rate: 38400 bd
40 track double density, 16 sectors of 256 bytes per track/side. This totals to 320 kByte per disk. A system disk, containing BOOT80.SYS (TF-20 boot file) and DBASIC.SYS (HX-20 Disk basic extension) has about 8 kByte less space.
An image (made with Teledisk is available.
The manual and schema are available from the mirror

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
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. mirror

Last update: 2009-12-18

fjkraan@xs4all.nl

Front		The TF-20 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. 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 is loaded, it can communicate to external devices like the HX-20 or PX-8. 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 flat cable connector is not used when the unit is configured as a HX-20 disk drive unit. There probably was another configuration like extra disk drives for a QX-10. Some specs: Serial interface baud rate: 38400 bd 40 track double density, 16 sectors of 256 bytes per track/side. This totals to 320 kByte per disk. A system disk, containing BOOT80.SYS (TF-20 boot file) and DBASIC.SYS (HX-20 Disk basic extension) has about 8 kByte less space. An image (made with Teledisk is available. The manual and schema are available from the mirror
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.