Sinclair ZX Spectrum
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| Sinclair ZX Spectrum – The Iconic Home Computer | |
| Specifications | |
|---|---|
| Manufacturer | Sinclair Research Ltd |
| Type | Home computer |
| Released | April 1982 |
| Discontinued | 1992 |
| Intro price | £125 (1982) |
| CPU | Zilog Z80A @ 3.5 MHz |
| Memory | 16 KB, 48 KB, or 128 KB RAM (varies by model) |
| Storage | External cassette tape (300 baud, EAR/MIC jacks) |
| Display | 256×192 pixels, 32 characters × 24 lines |
| Sound | Beeper (monophonic) |
| Dimensions | 23 cm × 14 cm × 4 cm (9.1" × 5.5" × 1.6") |
| Weight | 1.1 kg (2.4 lb) |
| OS / Firmware | Sinclair BASIC in ROM |
| Predecessor | Sinclair ZX81 |
| Successor | Sinclair ZX Spectrum+ |
| Codename | ZX Spectrum |
| Model no. | ZX Spectrum, ZX Spectrum+ |
The Sinclair ZX Spectrum is an 8-bit home computer released by Sinclair Research Ltd in April 1982. It became a defining product of the early home computing era in the UK, known for its distinctive rubber keyboard and vibrant color graphics. The ZX Spectrum sold over 5 million units and is credited with popularizing home computing and gaming in the UK.
Architecture
[edit | edit source]- CPU – Zilog Z80A microprocessor clocked at 3.5 MHz.
- ROM – 16 KB or 48 KB ROM containing Sinclair BASIC and system routines.
- RAM – Available in 16 KB, 48 KB, or 128 KB configurations, expandable via external RAM packs.
- Logic – Utilizes a combination of discrete logic and custom chips for video output and keyboard scanning.
Video generation
[edit | edit source]The ZX Spectrum generates video using a technique called "bit-banging," where the Z80 CPU directly controls the display output. The screen resolution is 256×192 pixels with a palette of 15 colors, plus black. The unique attribute system allows for color attributes to be assigned to 8×8 pixel blocks, resulting in colorful graphics but also potential color clash.
Storage
[edit | edit source]Data is loaded and saved via a standard cassette tape interface operating at 300 baud. The average loading time for a game is approximately 3-5 minutes, depending on the size of the program.
I/O and Expansion
[edit | edit source]- Edge connector (50-way) – provides access to the full Z80 bus, power, and video signals.
- 9 V DC input – unregulated power supply.
- Composite video output – for connecting to monitors and TVs.
Commercial peripherals included:
- ZX Printer, joystick interfaces, and various RAM expansion packs.
Known PCB Revisions & Errata
[edit | edit source]| Issue | Visible Clues | Key Fixes / Changes |
|---|---|---|
| Issue 1 (1982) | Original board layout with no solder mask. | • Early boards had issues with RAM stability; later revisions improved power distribution. |
| Issue 2 (1983) | Added solder mask and improved trace routing. | • Enhanced video output stability and reduced color clash issues. |
General Maintenance
[edit | edit source]| Issue | Cause | Remedy |
|---|---|---|
| Flickering display | Aging capacitors in the power supply | Replace with high-quality electrolytic capacitors. |
| Unresponsive keys | Worn rubber contacts on the keyboard | Replace keyboard or use conductive paint to restore contact. |
| Loading errors | Dirty cassette connectors | Clean connectors and ensure proper tape alignment. |
Regular maintenance, including cleaning the keyboard and ensuring proper connections, can help prolong the life of the ZX Spectrum.
Schematic & PCB
[edit | edit source]The complete schematic for the ZX Spectrum is available for enthusiasts and repair technicians.
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Common Modifications
[edit | edit source]- RAM upgrade – Adding external RAM packs to increase memory capacity.
- Composite video mod – For improved video output quality on modern displays.
- Keyboard replacement – Upgrading to a full-travel keyboard for better typing experience.
- Turbo mode modification – Overclocking the Z80 for faster performance (requires careful tuning).
ROM Keyword Map
[edit | edit source]Each key on the ZX Spectrum keyboard has multiple functions depending on the mode:
| Key | F mode |
K mode |
L mode
|
|---|---|---|---|
| P | PRINT |
P |
(
|
| R | RETURN |
R |
)
|
| G | GOTO |
G |
>
|
Edge-Connector Pin-out
[edit | edit source]| Pin | Signal | Description | Pin | Signal | Description |
|---|---|---|---|---|---|
| 1 | A15 | Address bus MSB | 26 | D4 | Data bit 4 |
| 2 | A14 | 27 | D5 | ||
| 3 | A13 | 28 | D6 | ||
| 4 | A12 | 29 | D7 | ||
| 5 | A11 | 30 | BUSACK | Bus acknowledge | |
| 6 | A10 | 31 | BUSRQ | Bus request | |
| 7 | A9 | 32 | WAIT | Insert wait-states | |
| 8 | A8 | 33 | HALT |