JVC Compu Link, a brief history of time and space

JVC Compu Link (also called SYNCHRO 'terminal') was a simple point to point or later disjointed daisy chain method of connecting many Audio (only) devices together in a chain of devices.Initially TAPE (Cassette), CD (player) and MD - MiniDisc (recordable) to each other and to an AMP (AM/FM Receiver, Amplfier, Source switcher with IR remote receiver).

The protocol seems to be based on a 8 bit data frame with stop (or possibly a Parity) bit, at 100 or 110 baud (bps) in which 3 bits represent a Device, and four bits represent a state or 'command' from or to an addressed device. The intial cable was described as a [monoaural Ring/Tip miniplug] carrying logic levels of 5 volts or 0 volts refrenced to Ring ground. And normally [High] meaning a Pull-Up resistor was used to maintain a reference when not transmitting data.

Compu Link had (four) generations starting from about the year 1991.

Compu Link - I (version 1) was described as having the ability to emit or receive a [Start or Source] command along the connection to other devices. If [Play] was pressed on an Audio device it would emit a [Switch to Source command indicating itself, to an assumed AMP connected through the Compu Link connection] the AMP would then switch its Source to the Device requesting attention and shutdown any other playing Source. Alternatively an AMP could issue a [Start or Play] command to a particular Device naming it in the first three bits of the data frame.

Compu Link - II (version 2) was described as having the same capabilities but layering on additional features, there by maintaining backwards support for previous Compu Link - 1 Devices connected to Compu Link - II terminal ports.

Compu Link - III (version 3) gained [Stand By] or [On/Off] feature allowing the AMP to place a device into an On or Off mode called Stand By.

Compu Link - IV (version 4) gained the ability to coordinate Record/Pause and Playback between Audio components, in which a recorder was loaded with blank media, record and pause buttons pressed and then a seperate source signal component was set to play, it would inform the AMP to switch to it as the source.. the AMP would inform the recorder that playback had begun and release the pause to begin recording.

The Compu Link terminal ports, or mini-plugs were mono-aural (only one Ring, so only one signal path per connection) and to connect one to an AMP only one per device was required, however to daisy chain from for example a TAPE, to CD player and then to an AMP the CD player would be expected to have two Compu Link terminals, one could be used for connection to the TAPE device and would convey its signals to the CD player which would also be connected by its second Comp Link terminal to the AMP.

Early AMPs were mostly AM/FM radio receivers which shared their speaker connections and allowed switching the source, later including advanced audio mixers for equalization and mixing signals. Compu Link made them intelligent and able to respond and command various Audio connected components. Including acting as a Master IR remote receiver which could relay commands from the IR remote along the Compu Link connections to the various Audio Devices with a single remote. note: it did not relay demodulated "IR" codes, as with some other manufacturers, rather it issued legitimate Compu Link protocol codes targeted for that type of connected Audio device.

When MD - "mini-disc" player/recorders came along the ability to copy and record signals to digitial media opened up the ability to Read and Write [TEXT] from areas of the Disc. For this a new version  of Compu Link called [TEXT Compu Link] using "bi-aural" mini-plugs or [Tip, Ring, Ring]  was created and made using a {green colored} jacket. Early AMPs supporting this displayed the TEXT on Vacuum Fluorscent Display tubes called (VFD). Later Audio/Video AMPs would display TEXT Compu Link in TV On Screen Displays integrated in the video display menus on the TV. Early methods of entering TEXT were performed using a Qwerty alphanumeric keyboard in the remote, and were later replaced by On Screen Display navigation of a Video keyboard on the TV screen using remote control arrow keys.

When Video source became available and an Audio/Video switcher was added to the AMP another new version of Compu Link called [AV Compu Link] using another set of mini plugs was created. There were three (I, II, III) versions of AV Compu Link. In addition TVs were given AV Compu Link terminal ports, and or Compu Link EX terminal ports. The functions included a similar ability to set the Video Source of the AMP (now called generically the Receiver) either by turning on a Video source, or by turning on the TV. The "Receiver" would then use the commands from the Video sourcer or the TV to set the appropriate paths for video and audio through the receiver to the TV for playback. Like MD, this began with VCR, DVD sources and progressed through recordable versions.

The Compu Link family of protocols were a Home Theatre set of protocols to coordinate signal source and choice using a central Master device called the AMP or Receiver which could also consolidate the remotes into one remote for the Receiver to control all of the other Audio and Video components to the Speaker and/or the TV display device.