Sinclair ZX80: Difference between revisions

The '''ZX80''' arrived in February 1980—just months before the BBC Micro project was even conceived—and became the '''first consumer microcomputer to retail for under £100''' in the United Kingdom.<ref>Mail-order advert, ''Practical Computing'', March 1980.

* Sinclair’s glossy national-press adverts boasted “The computer you can afford to own” and invited readers to “own a real computer for less than the price of a colour TV.”   

* Production was handled by Timex’s Scottish plant in Dundee; the first 10 000 boards were delivered in six weeks.   

* '''Estimated lifetime sales:''' contemporary interviews with Clive Sinclair quote “50–70 000 kits” and around “30 000 ready-built” units, giving an aggregate of '''≈ 100 000 ZX80s worldwide''' before the ZX81 superseded it in March 1981.

* '''CPU''' – Z80A-class microprocessor clocked at '''3.25 MHz''' (half the UK colour-burst for simple TV timing).   

* '''ROM''' – 4 KB mask ROM containing Sinclair Integer BASIC, line-editor and I/O routines.   

The Z80 itself bit-bangs UHF video: during the '''FAST''' display loop it outputs a sync pulse then immediately fetches the next character row from RAM, interleaving code and picture. When the CPU is diverted to BASIC interpretation the timing breaks, so the TV loses sync – producing the ZX80’s trademark flicker. (The later ZX81 added a SLOW mode with hardware assistance to cure this.)

* '''Edge connector (44-way)''' – exposes full Z80 bus, power and video lines.   

* '''9 V DC input''' – un-regulated (internally regulated to 5 V).   

: ''ZX Printer, joystick adapters, floppy-drive interfaces, composite video mods''.

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|+'''ZX80 Logic-Board Issues'''

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! Issue !! Cause !! Remedy

Full recapping, regulator heatsinking and replacement of the brittle membrane keyboard are popular reliability upgrades.

The complete single-layer PCB schematic is freely available   

* '''8 KB ZX81 ROM upgrade''' – drops-in to give floating-point BASIC, SAVE/LOAD VERIFY and better editing (still no SLOW mode).   

* '''Composite video mod''' – bypass RF can for crisp LCD/monitor output.   

* '''Turbo crystal (3.58 MHz)''' – simple Xtal swap for ≈10% speed gain (requires retune TV).

Each key performs multiple functions depending on mode:   

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|22 || '''VIDEO''' || Composite video out (TTL) || 44 || '''/RAMCS''' || Low = internal RAM enable

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|+'''ZX80 Address Space (standard 1 KB RAM)'''

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The ZX80’s display is entirely CPU-generated; during '''visible lines''' the Z80 executes a tight NOP/DJNZ loop to emit sync & pixel pulses on the ```VIDEO``` pin.

''Because the Z80 is busy generating video, '''user programs run only during the vertical blank'''; running BASIC therefore blanks the display, a quirk fixed in the later ZX81 by adding NMI-driven slow mode.''

* '''Guinness World Records''' recognises the ZX80 as the ''first computer sold for under £100'' (ready-built).   

* Featured (and exploded!) in the 2009 BBC dramatisation '''''Micro Men''''' depicting the rivalry between Sinclair and Acorn.   

* ZX80 BASIC token <code>'SLOW'</code> exists, even though the machine has no slow mode—left as vestigial code reused in the ZX81.   

* The iconic blue membrane keyboard’s legends were printed on *Woolmark-approved* polyester—the same supplier as Clive Sinclair’s electronic watch straps.

* [[Sinclair ZX81]] – successor with improved video logic.   

* [[Sinclair ZX Spectrum]] – coloured 1982 evolution of the Sinclair line.   

[[Category:Sinclair Computers]]