The Chroma 81 interface is a multi-purpose peripheral for the ZX81. Its primary function is to allow the ZX81 to be connected to a TV via a SCART socket to produce an RGB picture that is sharp and bright.
The Chroma 81 interface plugs into the expansion port of the ZX81 and connects to the TV using a standard SCART cable. There is no need to make modifications to the ZX81 since the Chroma 81 interface only requires access to those signals available on the expansion bus.
An exciting additional feature of the Chroma 81 interface is its ability to add colour to the ZX81 display. Two colour modes are provided, each supporting up to 15 colours. One mode provides an attributes file similar in concept to that found on the Spectrum. Use of this attributes file requires dedicated software to control it. The other mode provides a colour look up table that maps specific colours for each of the 128 different characters (64 normal and 64 inverse) that the ZX81 can display. This mode allows existing games to be colourised!
The Chroma 81 interface also provides the following facilities:
16K RAM pack.
8K RAM located between $2000-$3FFF, which allows support for user definable characters.
16K RAM pack located in the 48K-64K region of the memory map, which can be used for data storage.
Attribute colour mode (15 ink and 15 paper colours per character position).
Character code colour mode (15 ink and 15 paper colours per line of each normal and inverse character).
LOAD/SAVE sounds output through the SCART socket to the TV speaker(s).
Quicksilva Character Board emulation, which can be used with the Quicksilva games that supported the original board.
WRX hi-res graphics support for the onboard RAM.
RS232 socket, allowing connection to a variety of serial devices, such as a printer or a PC.
ZX Interface 2 style ROM cartridge socket, allowing the internal ZX81 ROM to be completely overridden.
Cursor joystick socket, with support for auto-fire joysticks.
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.
Onboard 5V regulator to prevent additional heat build up inside the ZX81.
The Chroma 81 interface measures 10cm by 10cm. The key items of the interface are shown labelled in the following photograph: