|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)
If an HX-20 doesn't want to work, try this:
|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.
|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
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:
Text (BASIC) transfer from HX-20 to PC:
Last update: 2022-04-18