The Epson HX-20


The cold start starts with the menu 1 MONITOR, 2 BASIC. The date and time can be set by pressing CTRL-@.

The HX-20 depends heavy on its internal battery. If this is empty, the machine will not start. Waiting some hours while leaving the adapter connected can solve this problem. Charging a completely empty battery takes 8 hours with the standard HOOAA? adapter. Once a battery is shorted (they usually are after all those years), the HX-20 will not work at all. Disconnecting the battery will work, but no printing or tape access is possible, as this uses more power as the adapter can deliver. Modern, cheap penlight rechargable batteries have similar capacity as the original sub-type-C batteries and could be used to get an fully functional HX-20.

If the menu shows garbage entries, the computer should be initialized. This means entering the date while the RAM is cleared.

The RAM is battery backed up, so programs typed in are retained even if the machine is switched off. Programs can be added to the startup meny with the TITLE command from Basic. Available memory can be checked with PRINT FRE() from Basic. This should be 12891 bytes for an unexpanded HX-20 and 29275 bytes for an HX-20 with an Expansion Unit.

The Basic is standard Microsoft Basic with some Epson specific commands. With an TF-20 floppy drive and a boot disk, Disk Basic extensions are available. The Monitor is a simple debugger/monitor for the main 6801 processor.

The power switch at the left of the machine is more a suggestion to the processor than a real switch of power. So actually all four combinations of ON-OFF and Active- Inactive are possible.


The Epson portable range are one of few computers having both an RS-232 and serial port. Both have special DIN connectors, for which cables for various applications were available. The serial port is used for the disk drive and the video interface. The RS-232 is a port for generic purposes.

The micro cassette drive is used from Basic and has some special commands for tape control WIND.

The printer is also controlled from Basic using the standard commands LPRINT and LLIST.


Several HX-20 extensions were available from Epson and third parties:

Internal ROM
Memory extension
The official memory expansion increased the RAM from 16 kByte to 32 kByte. Another ROM socket was also included. The HX-20 with expansion fitted exactly in the brown case, leaving no space for the mains adapter or micro cassettes.
Third party RAM extensions were inserted into the HX-20.
Disk drives
Epson created the TF-20 (Terminal Floppy) drive and Disk Basic as storage extension for the HX-20. The TF-20 is connected to the serial port. It is a specialised CP/M like system, which needed a boot file. When the file is loaded, the drive is available for the HX-20. When Basic is selected from the Menu, the serial port is probed for a TF-20. If this is available, the HX-20 tries to load a file DBASIC.SYS, the Disk Basic extension. Without it the disks are not accessible.
Video Interface
The Video interface allows 40x24 characters on a standard monochrome screen. The command SCREEN 1,0 (??) activates the interface. All output from the HX-20 is directed to the interface.


F.J. Kraan, 2004-05-02