Colortran Multi-Plex. A control protocol from Colortran circa 1984-1990. The slightly older brother of DMX512.

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History - CMX (sometimes called C-156) traces its beginnings to an innovative control console called Channel Track that Colortran unveiled in 1979. A digital data stream, sent from the CPU over a coaxial cable, was decoded by a local D/A converter into individual 0-10 volt analog levels. The protocol appeared in its present form in later designs, such as the Patchman, Dimension 5 and Prestige series consoles. These products utilized RS422 differential data transmission for remote D/A's or direct control of dimmers. CMX receivers included a 108-channel D/A card produced in the early to mid-1980s and the popular D192 high-density dimmer rack introduced in 1985. Virtually all control and dimmer products sold by Colortran were user-configurable for either CMX or DMX operation by 1989. As many people in the industry are aware, CMX protocol was the prototype for today's DMX512. The only major difference is the data rate, which was increased to 250 Kbaud for DMX. Interestingly, Colortran's design team foresaw the need for the protocol to talk to more than just dimmers, so they designated the first word of the data stream as an identifier for the type of information to follow (now DMX512's start code!).
Details - Two slightly different transmission speeds were used: 156.25 Kbaud for early systems and 153.6 Kbaud from about 1985 on. There's not enough difference between the two rates to matter, so a controller running at either speed will work with any dimmer rack. CMX pioneered the familiar 5-pin XLR and pinout later adopted by DMX512: shield/common on pin 1, data- on pin 2, data+ on pin 3. Some products such as Status consoles received their DC power from the dimmer pack on pin 5.
Interfacing Hints -- Problems may be encountered if you try to read and convert the CMX output from a Patchman console. This unit sent even parity instead of a second stop bit, which will confuse many receivers. Caution: before connecting new control equipment to an older Colortran dimmer, first ensure that no power supply voltages are present on pins 4 or 5.

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