Fender's Triad Interface
The following article is being reprinted from the August 1983 Polyphony magazine with permission. Contact paia@paia.com.
See the August 2004 ChromaTalk mailing list discussion ARP Digital Access Control which includes some Polaris documentation that throws doubt on what exactly was meant by "Triad."
The Chroma Keyboards division of Fender musical instruments has introduced a new instrument interface bus, called Triad (TM). This system lets users connect instruments to computers via a 25-pin D-connector cable; multi-instrument connections can be made by using one Triad device (for example, a Triad-equipped computer) as a star-network controller.
Triad-equipped instruments will have two uni-directional 8-bit parallel ports (one output, one input) and two handshaking lines for each port. This structure is intended to provide extra flexibility in the way that a Triad system responds to data. The handshaking lines can be polled or used to interrupt the Triad device.
The software characteristics of the Triad interface make it unique among instrument interfaces. Multi-byte operating commands are transferred across the bus, and the receiver interprets and acts upon those commands. All Triad-equipped devices that produce musical sounds are organized as logical instruments. The number of logical instruments available in the device can be communicated through the Triad interface.
The instrument consists of "channels" assigned to it and a data structure defining the sound of that instrument. The channels are the actual sound generation modules in the Triad device. The total number of channels available can change (due to adding expanders, etc.) and be communicated through the interface. The number of channels allocated to a particular instrument can be controlled through the Triad interface or automatically set by the Triad device when the instrument is defined.
All Triad-equipped devices are capable of receiving data to be acted upon at a future time. This is accomplished by using relative time commands. Each command can be preceded by a time command that tells a Triad device when to execute the command (relative to the last execution in that logical instrument). The time command values are in increments of 1/192 notes. Time synchronization between Triad devices is accomplished by beat commands that are sent only when the time base should be changed.
All Triad devices are capable of time stamping the commands representing performance and panel events. That is, the device can simulate a recorder or sequencer. The commands which control these functions are standardized and accessible from the Triad interface.
The Triad command structure permits device-dependent data to be transferred over the interface. A program that defines a sound, for example, can contain information useful to that particular device. The structure of other device-dependent command functions (such as the SERT PARAMETER function on a Chroma Polaris synthesizer) is standardized. But what the device actually does with this data is device-dependent. For example, SET PARAMETER 3 TO 0 could mean "set the keyboard algorithm to polyphonic" in a Chroma-type synthesizer; or "set the modulation index to 0" in a digital synthesizer. Also an escape command sequence is available for use with device-dependent functions to be developed in the future.
The Triad interface also provides other functions including "peeking" and "poking", or otherwise interrogating or changing the device's internal workings. Any cassette interface that the device controls can be accessed over the Triad interface. And commands relating to interface data flow control are also available. 