Sinclair ZX80

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Sinclair ZX80
Sinclair ZX80
Manufacturer Sinclair
Type Home computers
publication January 29, 1980
End of production 1981
Factory price 498 DM
processor Zilog Z80 @ 3.25 MHz
random access memory 1 KB , expandable to 16 KB
graphic 32 × 24 characters, monochrome
64 × 48 block graphics with graphic characters
Sound nv
Disk Audio cassettes
operating system Sinclair BASIC
successor Sinclair ZX81

The Sinclair ZX80 is a home computer from the British company Sinclair , it was released on January 29, 1980. It is the predecessor of the Sinclair ZX81 . The name ZX80 was derived from the name of the processor, supplemented with an "X" as a sign of a "mysterious ingredient".

The housing of the ZX80 is white and a bit clunkier than its black successor, the ZX81. The case of the ZX80 was designed by industrial designer Rick Dickinson. The Z80 - CPU is clocked at 3.25 MHz, which corresponds to the then state of the art.

The Sinclair ZX80 wanted to create a minimal system using a special feature of the Z80 microprocessor. In contrast to the Intel 8080 , with which it is compatible, this generates consecutive addresses on its address bus during its internal work cycles. These are intended to refresh dynamic memories ( DRAM ) cyclically. Sinclair used these refresh addresses for purposes other than those intended in order to continuously retrieve graphic data pixel by pixel from the main memory and display it on the screen. This saved a graphics module. The processor could either generate image data or compute internally. So the picture flipped over each time a key was pressed and during internal program processing and was then displayed again when input requests or program stops. This irritating effect led to the slow mode in the successor model ZX81. The processor could then do its arithmetic work in the horizontal and vertical blanking intervals, i.e. at all screen edges, while the screen signal was not being activated, which significantly reduced the working speed, but enabled a stable image. Higher integration of the building blocks made this possible.

The ZX80 is connected to the antenna socket of a television with a cable via the built-in RF modulator . Text with 32 columns and 24 lines is displayed there.

The character set does not conform to ASCII and contains letters and numbers as well as BASIC keywords . Most of the BASIC commands are entered with a single keystroke. Only a few functions like PEEK () and CHR $ () have to be entered letter by letter. This means that the programs only take up a small amount of space in the ZX80's relatively small main memory.

Inner workings of the Sinclair ZX80

There are a few differences between the ZX80 and its successor, the ZX81:

  • The read only memory (ROM) of the ZX80 is only 4  KB , that of the ZX81 is 8 KB.
  • The smaller ROM only enabled a smaller range of commands on the Sinclair BASIC than on the ZX81.
  • Unlike the ZX81, the ZX80 cannot yet calculate with floating point numbers . The integers of the ZX80 can have values ​​between -32768 and +32767 (16 bits).
  • The ZX80 still has 21 chips (discrete TTL components), the ZX81, however, gets by with five, later versions only contain four chips.
  • Since neither the ZX80 nor the ZX81 are equipped with a separate video controller, the main processor is also responsible for the screen display. While with the ZX80 keyboard inputs or the execution of basic commands and programs cause correspondingly long interruptions in the screen display, the ZX81 is by default in a SLOW mode, in which the arithmetic work only takes place during the blanking interval .

Otherwise the ZX80 and ZX81 are technically largely the same, so that further details on the ZX80 can be found in the article on the ZX81 . The ZX80 could be upgraded with the 8 KB ROM of the ZX81 and a matching new keyboard membrane, whereby the differences in language range and floating point numbers disappeared. This upgrade was also officially planned by Sinclair and the ZX81-ROM was specifically programmed so that it also worked in the ZX80. However, even a ZX80 that has been upgraded in this way does not know the SLOW mode, which can display a stable image (with reduced processing speed). For the experienced hobbyist, however, this can be retrofitted with little effort and the installation of a few more chips, so that the ZX80 can be upgraded to a full-fledged ZX81. However, because of its rarity, an original ZX80 has a significantly higher collector's value than an upgraded one.

Web links

Commons : Sinclair ZX80  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ Stephen Tomkins: ZX81: Small black box of computing desire . In: BBC News . March 11, 2011 ( bbc.com [accessed April 1, 2020]).
  2. ↑ Sinclair ZX 80/81 Rick Dickinson recalls. August 31, 2010, accessed April 15, 2020 .
  3. ↑ ZX80 / ZX81 / TS1000 composite video mods | ByteDelight.com. Retrieved April 15, 2020 (American English).