Editing Sinclair ZX Spectrum

{{Infobox computer
| name         = Sinclair ZX Spectrum
| image        = [[File:ZX_Spectrum.jpg|250px]]
| caption      = Sinclair ZX Spectrum – The Iconic Home Computer
| manufacturer = Sinclair Research Ltd
| type         = Home computer
| release date = April 1982
| discontinued = 1992
| 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           = Sinclair BASIC in ROM
| predecessor  = [[Sinclair ZX81]]
| successor    = [[Sinclair ZX Spectrum+]]
| codename     = ZX Spectrum
| model        = ZX Spectrum, ZX Spectrum+ 
| logo         = [[File:Sinclair ZX Spectrum-02b.svg|250px]]
}}

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 ==
* '''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 ===
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 ==
Data is loaded and saved via a standard cassette tape interface operating at approximately '''1500 baud'''. The average loading time for a game is approximately 3-5 minutes, depending on the size of the program.

== I/O and Expansion ==
* '''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 ==
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''ZX Spectrum PCB Revisions'''
! 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 ==
{| class="wikitable styled-table" style="width:70%; text-align:center;"
! 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 ==
The complete schematic for the ZX Spectrum is available for enthusiasts and repair technicians.  
{| class="wikitable"
|+
! [[File:ZX_Spectrum_Schematic.png|thumb|center|500px|ZX Spectrum circuit diagram]]
! [[File:ZX_Spectrum_PCB_Top.jpg|thumb|center|260px|Top view of the ZX Spectrum PCB]]
|}

== Common Modifications ==
* '''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 ==
Each key on the ZX Spectrum keyboard has multiple functions depending on the mode:  
{| class="wikitable styled-table" style="text-align:center;"
|+ Example ZX Spectrum keyboard layer
|-
! Key !! <code>F</code> mode !! <code>K</code> mode !! <code>L</code> mode
|-
| '''P''' || <code>PRINT</code> || <code>P</code> || <code>(</code>
|-
| '''R''' || <code>RETURN</code> || <code>R</code> || <code>)</code>
|-
| '''G''' || <code>GOTO</code> || <code>G</code> || <code>></code>
|}

== Edge-Connector Pin-out ==
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:75%; text-align:center;"
|+'''ZX Spectrum 50-way Expansion Bus (viewed from rear, component side up)'''
! 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'''
|}

[[Category:Sinclair Computers]]