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		Sinclair ZX81, (ZX81, Timex Sinclair 1000) a low-cost home computer developed by Sinclair Research and manufactured in Scotland by Timex Corporation, launched in the UK in March 1981, and as slightly modified Timex Sinclair 1000 in the US in July 1982. The ZX81 consists of a 3.5 MHz Z80A CPU from Nippon Electric Company, an ASIC dubbed Sinclair Computer Logic, an 8 KiB ROM with the operating system, the Sinclair BASIC interpreter, and one KiB of RAM, which could be expanded externally to 16 KiB. For I/O it had a membrane keyboard, a RF modulator to output 24 lines x 32 characters or 64x48 pixel as signal for a television, and a serial port and softmodem [1], to store and load programs and data to or from an external audio cassette recorder with 250 baud [2]. Jim Westwood's technical dodge using non-maskable interrupts solved the flicker problem of the ZX80 and gave the ZX81 a "multi-tasking" SLOW mode with a steady display [3], slowing down programs fourfold [4]. Z80 machine code could be inlined at absolute addresses and called via USR [5] or encoded in comment lines [6], which could be executed after some appropriate POKE instructions.
ZX81 setup [7]

Chess Programs

The only chess program for the non expanded ZX81 in SLOW mode was 1K ZX Chess by David Horne. Other programs, such as Artic Computing's ZX Chess, and Chris Whittington's SuperChess, require the 16 KB memory expansion.

ZX Chess [8]		1K ZX Chess [9]		SuperChess [10]

See also

• TRS-80
• ZX Spectrum

Publications

• ZX81 Assembly Instructions (pdf)
• ZX81 Assembly Instructions U.S. Version for UHF Channel 33 (pdf)
• Brendon Gore (1982). Interview-One Degree In Artic. Your Computer, May 1982
• David Horne (1982). ZX-81 Disassembler. Your Computer, July 1982
• Stuart Nicholls (1982). ZX-81 Games Writing. Your Computer, November 1982
• David Horne (1982). Chess in 1K. Your Computer, December 1982
• David Horne (1983). ZX-81 Chess. Your Computer, January 1983
• David Horne (1983). Full ZX-81 Chess in 1K. Your Computer, February 1983

Forum Posts

• World smallest chess program by Óscar Toledo Gutiérrez, comp.lang.c, November 22, 2006
• Turnier: Schachcomputer vergleich zu alte Computerschach Spiele by Spacious Mind, Schachcomputer.info Forum, August 12, 2008 (German)

External Links

• ZX81 from Wikipedia
• ZX80 from Wikipedia
• Timex Sinclair 1000 from Wikipedia
• List of ZX80 and ZX81 clones from Wikipedia
• ZX81 Home Page
• Sinclair ZX81 Page
• ZX81 Museum - Sinclair ZX81 Hardware, Software and Literature
• ZX81 circuit diagram
• Assembly Listing of the Operating System of the Sinclair ZX81
• 1K ZX81 Chess Z80 Assembly listing © Copyright David Horne
• Timex Sinclair 1000 - Old Home Computers Collection from The Spacious Mind
• ZX81 Software, Books and Hardware Collection
  Index of ZX81 Tapes by Artic
  Index of ZX81 Tapes by Mikro-Gen
  Index of ZX81 Tapes by Psion
  Index of ZX81 Tapes by Sinclair Research
  Index of ZX81 Tapes by Timex Sorted by Name

References

1. ^ Assembly Listing of the Operating System of the Sinclair ZX81 - THE 'SAVE COMMAND' ROUTINE, THE 'LOAD COMMAND' ROUTINE
2. ^ ZX81 from Wikipedia
3. ^ Assembly Listing of the Operating System of the Sinclair ZX81 - THE 'NON MASKABLE INTERRUPT' ROUTINE
4. ^ ZX81 from Wikipedia
5. ^ Stuart Nicholls (1982). ZX-81 Games Writing. Your Computer, November 1982
6. ^ David Horne (1982). Chess in 1K. Your Computer, December 1982
7. ^ A typical Sinclair ZX81 setup including cassette recorder and black-and-white television set, Photo by Mike Cattell, ZX81 from Wikipedia
8. ^ ZX81 Cassette Tape Information for ZX Chess I (Black inlay)
9. ^ ZX81 Cassette Tape Information for 1K ZX Chess
10. ^ ZX81 Cassette Tape Information for Super Chess

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