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Sinclair ZX Spectrum, Sinclair Ltd. UK

zxsp_100.png In April 1982 Sinclair presented the ZX Spectrum, their first colour model, the successor of the million seller ZX81.

The issue 1 machines were routed manually, giving the PCB a distinct look. The 32K Ram extension to full 48K was not soldered on the main PCB but on a add-on PCB which was mounted in the rear of the machine across the extension bus connector. Reportedly the machines crashed frequently on the first press presentation, making no real good impression, due to a timing problem between ULA (logics IC designed by Sinclair) and CPU memory access. This was fixed by a add-on PCB with a 74LS00 IC which was typically mounted top-side down - hence it's nikname "dead cockroach".

Only 60,000 issue 1 machines were built, making them a rare collectors item today. The very first machines (some thousands) had light grey rubber keys which were replaced quickly by slightly darker, bluish keys because the red keyword printing on the grey key tops was hard to read. Therefore today ZX Spectrums with the faint grey keyboard are very rare.

Issue 2 was still basically a 16K machine wich could be upgraded to full 48K by adding Ram and some logic ICs into sockets on the main PCB. Starting with issue 3 the ZX Spectrum was only produced as a 48K machine.

In 1984 the rubber keyboard Specci was replaced by the Sinclair ZX Spectrum+, which had a 'full travel' keyboard with plastic caps.

Technical Data

Model        Sinclair ZX Spectrum
Manufacturer Sinclair Research Ltd.
Production 1982 - 1984
CPU Z80A microprocessor running at 3.5 MHz
ROM 16K Rom containing Basic interpreter and operating system
Single-key keyword entry for Basic keywords
RAM 16K or 48K, thereof approx. 9K or 41K usable for programs
Keyboard 40 'moving' rubber keys
Display Graphics mode: memory-mapped screen file of 256 x 192 pixels.
No text mode: 32 x 24 characters are rendered in graphics mode.
Colour: One colour attribute byte per character square:
foreground colour, background colour, bright, flashing
15 colours: 8 normal and 8 bright colours. (the two blacks show no difference.)
Sound Internal loudspeaker driven by one i/o port bit.
Storage: Cassette tape interface: ~1500 bits/sec.
Dimensions 233 x 144 x 30 mm
Connectors PAL UHF colour TV out on channel 36
9V hollow plug power supply
Extension bus
3.5 mm mic and ear sockets to connect to a tape recorder


Name Letzte Änderung Länge 
BASIC Programming Manual/ 2020-08-27 14:08 61 
Circuit Diagrams/ 2020-08-27 14:08 16 
Current Selling Prices/ 2019-08-20 05:25 97 
HORIZONS Software Starter Pack (Sinclair)/ 2019-08-20 05:25 21 
Images/ 2019-08-20 05:25 33 
PCB Images (angled views)/ 2019-08-20 05:25
PCB Images (orthogonal)/ 2020-08-27 14:08 26 
Repair/ 2020-08-27 14:08 22 
ROMs/ 2019-08-22 19:20 16 
Tech specs/ 2019-08-20 05:25
BASIC Programming Manual.zip 2005-12-01 11:04 210060 
Introduction Manual.pdf 2005-12-01 11:08 870003 
ZX Spectrum BASIC programming (scanned by ST).pdf 2013-01-12 13:26 12563544 

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