Epson HX-20

The concept behind the HX-20 was first devised in July 1980 by Yukio Yokozawa, who worked for Suwa Seikosha, now the Seiko Epson subsidiary of the Japanese Seiko Group, receiving a patent for the invention.^[8] It was announced in 1981 as the HC-20 in Japan,^[1] and was introduced by Epson in North America as the HX-20 at the 1981 COMDEX computer show in Las Vegas, where it drew significant attention for its portability.^[9] It had a mass-market release in July 1982, as the HC-20 in Japan^[1] and as the Epson HX-20 in North America.^[2]

 

Epson advertised the HX-20 with a photograph and photo editing of the computer on two facing magazine pages with the headline "Actual size".^[10] With about the footprint of an A4 size page, the Epson HX-20 features a full-transit keyboard, rechargeable nickel-cadmium batteries, a built-in 120 × 32-pixel LCD which allowed 4 lines of 20 characters, a calculator-size dot-matrix printer, the EPSON BASIC programming language, two Hitachi 6301 CPUs at 614 kHz^[11] which is essentially an enhanced Motorola 6801,^[12] 16 kB RAM expandable to 32 kB, two RS-232 ports at a maximum of 4800 bits/s for the first 8-pin DIN connector intended for modem or serial printer with the second port capable of 38400 bits/s using a 5-pin DIN connector which was mainly for use with external floppy drive and video display^[11] an early concept of docking station, a 300 bit/s acoustic coupler was available,^[11] built-in microcassette drive, barcode reader connector.^[11] Uses a proprietary operating system, which consists of the EPSON BASIC interpreter and a monitor program, and weighs approximately 1.6 kg. The known colours of the machine are silver and cream, while some prototypes are dark grey. The HX-20 was supplied with a grey or brown carry case. An external acoustic coupler, the CX-20, was available for the HX-20, as was an external floppy disk drive, the TF-20, and an external speech synthesis Augmentative Communication Device (ACD), 'RealVoice'. Another extension was the serially connected 40 × 24 character video. It used a special protocol, EPSP,^[13] which was also used by the external floppy disk drive. The battery life of the HX-20 was approximately 50 h running BASIC and less using the microcassette, printer or RS-232.^[11] Data integrity could be preserved in the 4.0–6.0 V range.^[11] The power supply was rated for 8 W.^[11] Operating and charging it would tolerate 5–35 °C.^[11] Data integrity could be preserved at −5–40 °C.^[11] The HX-20 could be stored between −20–60 °C.^[11]

The later, more popular TRS-80 Model 100 line, designed by Kyocera, owed much to the design of the HX-20.

BYTE in September 1983 wrote that the HX-20, available in the United States for about a year, had been unsuccessful because of the lack of software or accessories. The review noted that Epson had included the formerly US$160 microcassette drive in the standard US$795 configuration, as well as bundling a simple word processor. BYTE praised the printer as "nothing short of amazing", but criticized the lack of an operating system for cassette storage and said that compared to the TRS-80 Model 100's display, "the HX-20 looks primitive".^[14]

The LCD is 120×32 pixels and is controlled by six μPD7227^[15] LCD controller ICs each responsible for 40×16 pixels of the LCD. The μPD7227 uses a serial protocol and has two memory banks for switching between rows 0-7 and 8–15. It features multiple modes, including "Write", "Read", "AND", "OR" and "Character". The "character" mode draws characters from a built-in character map. Each bank is 40 bytes, with a bit 6 of the address determining the bank. Even though the address can be up to 127, nothing will happen when trying to access data outside the banks. If the pointer action in a command is set to decrement and the pointer is at 0, the pointer will wrap to 127.

 

The Monitor program can be accessed via the main menu on startup by pressing 1, by typing the command "MON" in BASIC or by causing a trap, i.e. writing/reading to/from protected addresses or executing an illegal instruction. In the case of a trap, "Trap!" will be displayed in the Monitor and the user can use it for debugging.

When entering Monitor it shows a prompt on the first line, "Trap!" on the second line (if entered via a trap) and the CPU registers as they were right before the Monitor was entered on the third and fourth lines. These registers are A (Accumulator A), B (Accumulator B), X (Index Register), C (Condition Code Register), S (Stack Pointer) and P (Program Counter).

The monitor can be used for reading and writing memory, modifying CPU registers, running code at specific addresses in memory, saving/loading memory to/from a plugin option, etc. This is very useful for debugging programs written in machine code in difference to programs written in the EPSON BASIC programming language.

ROM #0 and #1 are known as the I/O ROMs, handling system reset and providing functions for using the LCD, keyboard, clock, printer, speaker, serial communication, etc. The I/O ROMs are equivalent to the BIOS in modern PCs. ROM #0 also contains the interrupt vector table at FFF0-FFFF. FFFE-FFFF determines what the program counter should be set to on power up or reset. In the standard set of ROMs for the HX-20, this value is E000, the start of ROM #0.

ROM #2 and #3 contains the BASIC interpreter. If the BASIC ROMs are removed from the motherboard, the BASIC option in the main menu will disappear, leaving only MONITOR. This is because ROM #3 contains a program header which is detected by the menu routines. This works the same for all user-created programs, except the program type is different.

The expansion unit added up to 16 KB of RAM and two ROM sockets. The latter could only be used by switching off the internal BASIC ROMS.^[16]

• HC-80 (Japanese version of the PX-8)
• HC-88 (Japanese version of the PX-8)
• HX-40 (American version of the PX-4)
• HX-45 (American version of the PX-4)
• KX-1
• PX-16 (IBM PC compatible portable, cartridges compatible with PX-4)
• PX-4 (successor of the HX-20, with larger screen and CP/M compatible like the PX-8)
• PX-8 (Geneva)
• EHT-30, EHT-40

• Epson ActionNote

 

Wikimedia Commons has media related to Epson HX-20.

• Epson HX-20 documentation, photos and software
• Epson's HX-20 manual and additional material
• HX-20 utility and game programs
• 'HXTape' program to read and write tapes via a soundcard
• old-computers.com article on the HX-20 Archived 2010-03-30 at the Wayback Machine
• 1983 Epson HX-20 computer., (evaluation) David H. Ahl., CREATIVE COMPUTING VOL. 9, NO. 3 / MARCH 1983 / PAGE 101
• vintage-computer.com article about the HX-20
• https://www.youtube.com/watch?v=o-F_hL1bZsw The World's First Laptop – Epson HX-20 / HC-20