Yet another computer museum - The Epson HX-20

Top Epson HX-20 top Standard 16 kByte RAM, here with the expansion unit, another 16 kByte. All battery operated.
More info in this announcement from Practical Computing magazine October 1982.
Targeted as a field terminal it found other uses like wordprocessing. The successor was the PX-8 which combined advantages from the QX-10 (CP/M, wide screen) with the HX-20 portability.

Inside Epson boards usually have names. The HX-20 board name is 'MOSU'.
The BASIC 'PRINT FRE(0)' command should return 12891 bytes free for a non-expanded HX-20.
The standard ROMs map from 8000h to FFFFh, the empty socket is for the option ROM (6000h-7FFFh)
Troubleshooting
If an HX-20 doesn't want to work, try this:

Charge the HX-20 for several hours. To charge from empty to full batteries takes 8 hours.
Make sure the batteries are actually charged. If after charging several hours the voltage over the battery is still 4 volts or below, your battery is shorted. An easy indication of this is the temperature of the adapter. If it is still hot after 8 hours charging, the battery is dead. Replace it before continuing.
An initialised HX-20 displays this on startup:
CTRL/@ Initialize 1 MONITOR 2 BASIC
If this doesn't happen, or more lines are printed, press CTRL and @. Then you should enter the date and time. The HX-20 should now work.

Expansion unit board The Expansion Unit contains 16 kByte RAM, constructed of eight 2kByte static RAM chips. The two ROM sockets are default empty. With the Expansion Unit connected, and no programs loaded the BASIC 'PRINT FRE(0)' should return 29275 bytes free (use Ctrl-@ to initialize). See the memory map for more info on the HX-20 memory map with and without the Expansion Unit.
More information is in the HX-20 Technical Support Manual, see Virtual Library or Using the Epson HX-20 expansion unit

ROM Cartridge The cassette bay could also be used for the ROM cartridge. A 32 kByte max ROM can contain up to 32 files which are listes and read via the FILES "PAC0:" and LOAD "PAC0:filenaam" commands in Basic. Other ROM structures were also possible, but would need additional software.
This ROM is not directly mapped into memory, data is loaded into memory first.
HX-20 ROM cartridge; file format

Batteries Nowadays not much of the original battery packs for the HX-20 will be in good working order. With some trouble and quite a sum of money, you can still buy replacements or make one yourself from NiCD C-cells. For operating the HX-20 only once in a while, this is not very cost effective. Replacing the internal pack with an external set of modern penlight (AA) NiHM cells works just as good, but has its price; making an extra hole or leaving out the connector pane. The battery is an essential part of the power supply; charging keeps the adapter voltage in check. Without it, the voltage on the circuit board becomes much too high and using power hungry peripherials lead to the 'CHARGE BATTERY!' message.

Disk drive unit Another expansion option of the HX-20 is the TF-20 floppy disk unit. This unit needs a floppy to load its own OS (CP/M) into RAM, and then could serve as disk drive for the HX-20, PX-8 or PX-4. The HX-20 retrieves a disk basic extension from the drive when entering BASIC. See the Epson TF-20 page for more info on the TF-20.
From the HX-20 Software Reference Manual Chapter 10.4):
The DISK BASIC is broadly divided into the following 3 modules: (1) BASIC interpreter (ROM version: HX-20 side) (2) DBASIC interpreter (DBASIC.SYS: HX-20 side) This interpreter is an extended portion of BASIC which is loaded from a disk to the RAM of the HX-20 upon start of the BASIC and handles the data input/output to and from the disk and the processing of the commands and statements, together with the BASIC interpreter described in (1) above. This module consists mainly of a portion connected to the BASIC interpreter (i.e., a BASIC driver) and a portion interfacing with the TFDOS (i.e., EPSP driver). (3) TFDOS (TF-side) The TFDOS which is resident on the RAM of the TF-20 received commands from the HX-20, opens and reads or writes files using the BDOS or the BIOS for the HX-20, and returns data and error codes to the HX-20.

Printer ERC-09B printer ribbon cartridge The printer uses a ribbon cartridge found in lots of small Epson printers and show up at Ebay regularly. It can also be used for PX-4 and PX-16 printers.

Connect to PC
HX-20 PC PC 8-pin DIN 9-pin subDE 25-pin subDB function 1 -------- 5 ----------- 7 GND 2 -------- 2 ----------- 3 HX-20 TxD, PC RxD 3 -------- 3 ----------- 2 HX-20 RxD, PC TxD 7 -+ 4 -+ | | RTS - CTS loop 8 -+ 5 -+ 6 -+ 6 -+ | | 1 -+ 8 -+ DSR, CD, DTR loop | | 4 -+ 20 -+
RS232C connector pin numbering
To connect the HX-20 to a PC, I use an Epson #705 cable, a gender changer, a null modem adapter and a 25p to 9p adapter. In essence it boils down to this diagram. Note that the DIN pin numbering is not regular.
Text (BASIC) transfer from PC to HX-20:

set serial port speed to 1200 Baud: Linux: sudo /bin/stty -F /dev/ttyUSB0 ospeed 1200 ispeed 1200
enter into HX-20: LOAD "COM0:(48N1F)" <ENTER>
send file: Linux: sudo cat fileName > /dev/ttyUSB0 and wait for it to finish
press <BREAK> on HX-20. The program is now loaded.

Text (BASIC) transfer from HX-20 to PC:

start terminal program and set serial port to 4800 Baud
start text capture mode
enter into HX-20: LIST "COM0:(68N1F)" <ENTER> and wait for it to finish
save captured text
On the command line, cat /dev/ttyX > list.txt might also work. Replace ttyX by your serial port

Local links:

Announcement in Practical Computing October 1982,
Wordprocessors for the HX-20,
Scanned and PDFed doc,
ROM contents and how to retrieve it,
Information on the HX-20 memory configurations,
Info on the HOOAAG adapter,
Info on the QX-10 computer,
Info on the PX-8 computer. An newer machine of similar architecture, but CP/M based,
Info on the PX-4 computer, The PX-4 can be seen as the successor of both the HX-20 and PX-8,
Info on the TF-20 disk drive system. A CP/M based disk station,
Info on the Epson RS-232C and SERIAL port cables,
Epson serial protocol for external devices like disk drives and monitors (preliminary),
Epson type numbers and codes.

Generic links:

HX-20 emulator on the site of TAKEDA, toshiya. It should work with the ROMs, but untested as yet. For now just BASIC is supported, tape and TF-20 support is expected later this year (2011)
Norbert Kehrer created a combined TF-20 and Video Display Unit emulator for the HX-20.
Epson USA HX-20 Doc,
An HX-20 Enthusiast's Page,
HXTape Reading and writing tapes.
Description of the KK Systems video interfaces for the HX-20
Info and BASIC programs
Information and Tools for the Epson HX-20

Last update: 2020-03-14

fjkraan@xs4all.nl

Top		Standard 16 kByte RAM, here with the expansion unit, another 16 kByte. All battery operated. More info in this announcement from Practical Computing magazine October 1982. Targeted as a field terminal it found other uses like wordprocessing. The successor was the PX-8 which combined advantages from the QX-10 (CP/M, wide screen) with the HX-20 portability.
Inside		Epson boards usually have names. The HX-20 board name is 'MOSU'. The BASIC 'PRINT FRE(0)' command should return 12891 bytes free for a non-expanded HX-20. The standard ROMs map from 8000h to FFFFh, the empty socket is for the option ROM (6000h-7FFFh) Troubleshooting If an HX-20 doesn't want to work, try this: Charge the HX-20 for several hours. To charge from empty to full batteries takes 8 hours. Make sure the batteries are actually charged. If after charging several hours the voltage over the battery is still 4 volts or below, your battery is shorted. An easy indication of this is the temperature of the adapter. If it is still hot after 8 hours charging, the battery is dead. Replace it before continuing. An initialised HX-20 displays this on startup: CTRL/@ Initialize 1 MONITOR 2 BASIC If this doesn't happen, or more lines are printed, press CTRL and @. Then you should enter the date and time. The HX-20 should now work.
Expansion unit board		The Expansion Unit contains 16 kByte RAM, constructed of eight 2kByte static RAM chips. The two ROM sockets are default empty. With the Expansion Unit connected, and no programs loaded the BASIC 'PRINT FRE(0)' should return 29275 bytes free (use Ctrl-@ to initialize). See the memory map for more info on the HX-20 memory map with and without the Expansion Unit. More information is in the HX-20 Technical Support Manual, see Virtual Library or Using the Epson HX-20 expansion unit
ROM Cartridge		The cassette bay could also be used for the ROM cartridge. A 32 kByte max ROM can contain up to 32 files which are listes and read via the `FILES "PAC0:"` and `LOAD "PAC0:filenaam"` commands in Basic. Other ROM structures were also possible, but would need additional software. This ROM is not directly mapped into memory, data is loaded into memory first. HX-20 ROM cartridge; file format
Batteries		Nowadays not much of the original battery packs for the HX-20 will be in good working order. With some trouble and quite a sum of money, you can still buy replacements or make one yourself from NiCD C-cells. For operating the HX-20 only once in a while, this is not very cost effective. Replacing the internal pack with an external set of modern penlight (AA) NiHM cells works just as good, but has its price; making an extra hole or leaving out the connector pane. The battery is an essential part of the power supply; charging keeps the adapter voltage in check. Without it, the voltage on the circuit board becomes much too high and using power hungry peripherials lead to the 'CHARGE BATTERY!' message.
Disk drive unit		Another expansion option of the HX-20 is the TF-20 floppy disk unit. This unit needs a floppy to load its own OS (CP/M) into RAM, and then could serve as disk drive for the HX-20, PX-8 or PX-4. The HX-20 retrieves a disk basic extension from the drive when entering BASIC. See the Epson TF-20 page for more info on the TF-20. From the HX-20 Software Reference Manual Chapter 10.4): The DISK BASIC is broadly divided into the following 3 modules: (1) BASIC interpreter (ROM version: HX-20 side) (2) DBASIC interpreter (DBASIC.SYS: HX-20 side) This interpreter is an extended portion of BASIC which is loaded from a disk to the RAM of the HX-20 upon start of the BASIC and handles the data input/output to and from the disk and the processing of the commands and statements, together with the BASIC interpreter described in (1) above. This module consists mainly of a portion connected to the BASIC interpreter (i.e., a BASIC driver) and a portion interfacing with the TFDOS (i.e., EPSP driver). (3) TFDOS (TF-side) The TFDOS which is resident on the RAM of the TF-20 received commands from the HX-20, opens and reads or writes files using the BDOS or the BIOS for the HX-20, and returns data and error codes to the HX-20.
Printer		The printer uses a ribbon cartridge found in lots of small Epson printers and show up at Ebay regularly. It can also be used for PX-4 and PX-16 printers.
Connect to PC	HX-20 PC PC 8-pin DIN 9-pin subDE 25-pin subDB function 1 -------- 5 ----------- 7 GND 2 -------- 2 ----------- 3 HX-20 TxD, PC RxD 3 -------- 3 ----------- 2 HX-20 RxD, PC TxD 7 -+ 4 -+ \| \| RTS - CTS loop 8 -+ 5 -+ 6 -+ 6 -+ \| \| 1 -+ 8 -+ DSR, CD, DTR loop \| \| 4 -+ 20 -+	To connect the HX-20 to a PC, I use an Epson #705 cable, a gender changer, a null modem adapter and a 25p to 9p adapter. In essence it boils down to this diagram. Note that the DIN pin numbering is not regular. Text (BASIC) transfer from PC to HX-20: set serial port speed to 1200 Baud: Linux: sudo /bin/stty -F /dev/ttyUSB0 ospeed 1200 ispeed 1200 enter into HX-20: LOAD "COM0:(48N1F)" <ENTER> send file: Linux: sudo cat fileName > /dev/ttyUSB0 and wait for it to finish press <BREAK> on HX-20. The program is now loaded. Text (BASIC) transfer from HX-20 to PC: start terminal program and set serial port to 4800 Baud start text capture mode enter into HX-20: LIST "COM0:(68N1F)" <ENTER> and wait for it to finish save captured text On the command line, `cat /dev/ttyX > list.txt` might also work. Replace ttyX by your serial port