Epson HX-20

Laptop computer released by Epson in 1981

The HX 20 (also known as the HC 20) is an early laptop released by Seiko Epson in July 1982. It was the first notebook sized portable computer, occupying roughly the footprint of an A4 notebook while being lightweight enough to hold comfortably with one hand at and small enough to fit inside an average briefcase. Despite praise from journalists for its technical innovations, the computer was not a commercial success outside of Japan. Radio Shack's TRS 80 Model 100 (the American version of a Kyocera notebook), released in 1983, is thus credited as the first commerically successful notebook computer.

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. It was announced in 1981 as the HC 20 in Japan, It had a mass market release in July 1982, as the HC 20 in Japan 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 6309 CPUs at 614 which is essentially an enhanced Motorola 6801, 16 RAM expandable to 32, two RS 232 ports at a maximum of 4800 for the first 8 pin DIN connector intended for modem or serial printer with the second port capable of 38400 using a 5 pin DIN connector which was mainly for use with external floppy drive and video display which was also used by the external floppy disk drive. The battery life of the HX 20 was approximately 50 running BASIC and less using the microcassette, printer or RS 232.

The LCD is 120×32 pixels and is controlled by six μPD7227 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 bit 6 of the address determining the bank and 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). 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.

Command Syntax Description S (Set) Writes the 8 bit value "new" (in hex) to 16 bit address <addr>. Entering only the address and pressing enter will make the old value at the address appear and the cursor put after the old value for entering a value. D (Dump) Dumps the values from addresses <addr> to <addr + 14> to the display. G (Go) Sets the programme counter to the 16 bit address <addr> and will return to Monitor before the breakpoint address <breakpoint> is executed. X (Examine) Allows the user to display and change the contents of each register. The RETURN key applies the changed value (if any) and jumps between registers. Typing a non hexadecimal character exits this command. R (Read) Transfer data from an external storage to memory. <device> can be any of M (microcassette), C (external cassette) and P (ROM cartridge). The memory address is specified using the "A (Address)" command. W (Write) Transfer data from memory specified by the "A (Address)" command to an external storage. See "R (Read)" for more information. ROM cartridge is not supported by this command. V (Verify) Verifies data transferred to an external storage against the memory specified by the "A (Address)" command. See "R (Read)" for more information. ROM cartridge is not supported by this command. A (Address) Specify an address range for commands R, W and V. The user will be prompted with T (Top address), L (Last address), O (Offset value) and E (Entrypoint). Offset and entrypoint values are only used by the "W (Write)" and "V (Verify)" commands. K (Key set) Enter a sequence of keys to be pressed automatically on power up (and reset). Press CTRL+@ to stop. A maximum of 18 characters can be entered and function keys counts as two characters. B (Back) Return to the procedure from which Monitor was called.