The SPECTRA interface is a multi-purpose peripheral for the 16K/48K ZX Spectrum. Its primary function is to allow the Spectrum to be connected to a TV via a SCART socket to produce an RGB picture that is sharp, bright and free from dot-crawl. An upgrade to the interface allows it to be used with the Spectrum 128/+2 in addition to the 16K/48K Spectrum (the Spectrum +2A/+3 require an adapter board to remap various signals on the expansion bus). This upgraded interface is named SPECTRA+128.
For simplicity, the rest of this website refers to both versions of the interface as just SPECTRA. The name SPECTRA+128 is only used when describing information specific to the upgraded board.
The SPECTRA interface plugs into the expansion port of the Spectrum and connects to the TV using a standard SCART cable. There is no need to make non-standard modifications to the Spectrum since the SPECTRA interface only requires access to those signals available on the expansion bus. The Spectrumís beeper sound is also directed through the SCART connection to allow it to be heard loud and clear through the TV speaker(s). The clarity of picture and sound is similar to that obtained when using a Spectrum emulator.
An exciting additional feature of the SPECTRA interface is its ability to extend the Spectrumís display to support 64 simultaneous colours and at a variety of increased vertical and horizontal resolutions, resulting in a total of 32 different display modes. At long last, the limited colour abilities of the Spectrum can be overcome, opening the potential for new visually stunning programs. In its highest resolution mode, the smallest block of clash-free colour becomes just 1 pixel high by 2 pixels wide when using a basic 8 colour palette!
Support is also provided for double buffering via two screen banks, similar in concept to that featured on the 128K Spectrum models. When SPECTRA+128 is used on a 128K Spectrum it becomes possible to output one of the screen banks through the SCART socket and the other through the Spectrum's built-in RGB socket, allowing the potential for programs to support dual displays!
The SPECTRA interface also provides the following facilities:
- A Kempston joystick socket, with support for auto-fire joysticks.
- A ZX Interface 1 compatible RS232 socket, ideal for connecting to a printer, modem or a PC.
- A reset button.
- Optional support for a ZX Interface 2 ROM cartridge socket.
- Optional support for an onboard ROM to override the Spectrumís internal ROM.
- The ability to extend Spectrum BASIC via a ZX Interface 1 compatible paging mechanism (offering the potential to extend BASIC with commands to drive the new display modes).
- A rear, full width gold plated expansion bus.
- A set of configuration switches to allow each new facility to be enabled / disabled, ensuring full I/O compatibility with all existing hardware, e.g. ZX Interface 1, ZX Interface 2, divIDE 57c.
The SPECTRA interface measures 10cm by 10cm. The key items of the interface are shown labelled in the following photograph:
All features come as standard, apart from the ROM cartridge and onboard ROM facilities which are mutually exclusive. When the onboard ROM facility is used, it is possible to fit a Zero Insertion Force (ZIF) socket which can be useful when developing custom ROM software. On the original SPECTRA interface it is left open for the user to fit / request whichever socket (if any) they prefer; on the SPECTRA+128 interface a ROM cartridge socket is fitted by default.
The 64 colour palette available with the new display modes is shown below. Six bits are used to define each colour, with 2 bits used per red, green and blue component.
The SPECTRA+128 interface can be used with the Spectrum+2A and Spectrum+3 via the SPECTRA+3 Adapter board, shown in the following photograph:
The SPECTRA interface was released on 22nd June 2012, with the SPECTRA+128 upgrade released on 14th May 2015, and the SPECTRA+3 Adapter released on 3rd July 2016.