We live and breathe this stuff on a daily basis in our company, and as a result, over the past decade or so have amassed a fair amount of practical experience. Now's our chance to share some of it with others!
The following article appeared in ESTA's Protocol, Fall 2000 issue, and is reprinted with permission.
© 2000 Entertainment Services & Technology Association.
In the previous article (Protocol, Spring 2000 Issue), we discussed some aspects of the evolution of lighting control protocols in our industry and standardization efforts that followed periods of "chaos". This time we'll get specific about proprietary multiplex protocols. We live and breathe this stuff on a daily basis in our company, and as a result, over the past decade or so have amassed a fair amount of practical experience. Now's our chance to share some of it with others!
Proprietary multiplex protocols are the manufacturer-specific console-to-dimmer data communication schemes that preceded establishment of the universal DMX512 standard. Most of these protocols came into being in the early 1980s, which, for better or worse, coincided with good times in the entertainment and architectural lighting markets. Dimmer-per-circuit systems became the industry standard. Everyone was using microprocessors. A lot of consoles and dimmers were sold!
Nearly 20 years later, most of those consoles are gone, but the vast majority of dimmer racks and packs are still in service, and will probably remain so for another decade or more. Why? Because, on the whole, they were built well and pretty much in line with the conventional technology you'd find in today's dimmers. Not only that, but dimmer racks are by far the most expensive items to purchase and install in a lighting system. And most people, given the opportunity, would rather allocate a limited equipment replacement budget to a better control console and other goodies such as new lights and color scrollers. These things you see and handle every day; the dimmers are out of sight and mind in the electrical dungeon! As long as the lights keep fading up and down, the racks will stay put.
But keeping those dimmers working means that, when a new control console is purchased, its DMX output must be translated to whatever the dimmers' native language is. In some cases, Colortran's D192 dimmer racks for example, the rack's control electronics can be modified to receive DMX512. This works fine most of the time, but the modified receiver tends to be pretty fussy about the DMX flavor it will accept. The house console may work fine, but the one that arrives with the next tour might not. The best all-round solution is to purchase a protocol converter with the new console. A good converter will receive any DMX signal that is within the parameters specified by the USITT DMX512 standard, and output the exact protocol required by the old dimmer racks.
Installing a protocol converter isn't always the best option, however. For example, if a rack's control electronics give constant trouble or simply won't work with converters, they can be replaced with a retrofit kit incorporating the latest technology and DMX512 inputs. But if the entire rack is a perpetual service problem, complete replacement is likely the only option.
As I wrote previously, most companies did their own thing when it came to dimmer control protocols, either ignoring what the rest were doing or figuring that their scheme was the superior one. A classic case of the not-invented-here syndrome if ever there was one. In retrospect, it's amazing that there were so many different philosophies and so little attention to standardization, all in such a relatively small industry where all the players were well known to each other.
In this article we'll focus on nine of these control protocols. Of course there were others around, for example ADB's S20, Major's Magnus, R.A. Gray's SDX, and TTI's C105 protocols. But we're not allowed to take over the entire journal, so we'll arbitrarily decide which ones are the most common and therefore more deserving of attention! So here we go, in alphabetical order:
AMX192 and D54
History - Strand's extremely popular Light Palette consoles and CD80 dimmers first appeared in 1979, and with them came a new multiplexed analog control scheme that would later evolve into USITT AMX192. It was soon incorporated into Mantrix consoles and Environ architectural dimmers; in fact, virtually every North American Strand product designed until very recently included at least one AMX port. As well, a number of their competitors made compatible products over the years. Strand's R&D group in the U.K. devised a somewhat different analog mux protocol they designated D54 (an internal standards number) to work with their Galaxy and Gemini control desks. D54 never made inroads into North America, but it ended up everywhere else in the world. On the other hand AMX192 is virtually non-existent outside of the U.S. and Canada, yet it was applied to a wide range of dimming and control product over the years, by a number of different designers and manufacturers. An unfortunate consequence is that many of these products are not entirely interoperable, even within Strand's own product lines.
Details - Depending upon the type of console, a single AMX192 data line can handle either 96 or 192 dimmers. Dimmer levels are sent sequentially on one wire, referenced to a signal common wire that the other conductor is paired with. A synchronizing clock signal is sent differentially on a second pair of wires. When AMX first appeared on Strand products, it used the tiny Switchcraft TA4 connector. Its pinout was clock- on pin 1, common on pin 2, clock+ on pin 3 and mux analog on pin 4. Suffice it to say (with understatement) that the TA4 was not the greatest connector choice Strand ever made. Many users, especially rental shops, couldn't wait to replace it with the tougher 4-pin XLR. If they'd waited a bit longer, though, they would have had a standard XLR sex and pinout provided by USITT in the AMX192 standard that appeared in 1985. Instead, there's a lot of gear out there that uses the wrong connector sex and the TA4 pinout. This is how it should be: input connectors are female and outputs are male; pin 1 is common, pin 2 is clock+, pin 3 is analog, and pin 4 is clock-.
D54 is easier to describe; it runs over 2 wires, a signal conductor that carries both the dimmer levels and the clock signal, and signal common. it uses only 3-pin XLRs and one pinout: common on pin 1, no connect on pin 2 and signal on pin 3. 384 dimmers are supported.
Both AMX192 and D54 use 0-5 volt dimmer levels.
Interfacing Hints - Anyone who has dealt with AMX192 gear for any length of time will tell you that they've had more than their share of problems getting things to communicate properly. No one console, for example, will talk to all receivers out there, and vice versa. The age and condition of receiver cards and power supplies can affect how well the data link works. The type and length of cable can also be a factor when changing to a different transmitter, such as a protocol converter. Just because your old Mantrix worked fine with your old CD80, it doesn't mean your new converter is no good because it doesn't. Designers of new AMX controls usually pick a set of signal timing parameters that are known to work well with most of the existing dimmer racks; you might just be one of the unlucky ones that gets a mismatch. Ask your supplier to let you test other makes of converters; at least one is likely to do the job.
History -- Possibly the earliest digital lighting control protocol to appear was from Avab of Gotheberg, Sweden. In the late 1970s, the company developed an asynchronous digital output card for their 2000 series console (later known as the Viking), which could communicate with a remote analog demultiplexer. In 1980 the technology was applied to the DD-I digital dimmers being designed in the U.S. By the time the DD-II dimmers were introduced in 1982, most of Avab's equipment utilized this protocol. DMX512 outputs were applied to the company's products beginning in 1990. There remains a huge base of Avab dimmers throughout the world (mainly in Europe) that operate exclusively on Avab protocol.
Details - Avab protocol runs at 153.6 Kbaud and 8-bit resolution. FFh is reserved as a frame header, so the maximum signal level is FEh (decimal 254). Early control consoles sent 128 dimmers per packet, later increased to 240. The Expert series consoles were capable of sending 252 dimmer levels. RS422 was used for the data link. All consoles sold in North America were modified to incorporate a "console present" output, which, by changing from a high to a low state, signals the dimmer racks that the console is sending valid dimmer data. The dimmer rack data connection used either a DB25 or circular connector with the following pinout: common on pin 7, data+ on pin 8, data- on pin 9, and console present on pin 12.
Interfacing Hints - There is a design error in the newer DD-IIB dimmers which requires that the data pair be swapped, that is, D- on pin 8 and D+ on pin 9. If the protocol converter doesn't have a console present output, the function may be disabled at the dimmer by turning on DIP switch B8. Other than that, protocol interfaces for Avab usually work right out of the box.
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.
History -- Electro Controls entered the digital protocol race in 1983. Originally known as "Celebrity Protocol" after the console that it was developed for, ECmux was used to control QD Series dimmer racks and Playmate digital packs. The protocol was expanded in 1985 to carry channel/dimmer softpatch information when Premiere control consoles were introduced, and the QD dimmer rack electronics were redesigned to store and process the patch data. Although very few Premieres were sold before Strand acquired EC in 1986 and stopped making that product, Celebrity consoles and QD racks continued to be manufactured under the name Strand Electro Controls. An updated Celebrity Plus appeared in the late 1980s; it transmitted patch data to the dimmer racks in the same fashion as the Premiere console. By 1992, Strand had stopped production of all EC-designed equipment except a new Premiere architectural control system.
Details - ECmux was an asynchronous protocol operating at 187.5 Kbaud and 8-bit resolution. Oddly, while the rest of the industry adopted RS422, EC employed a single-ended (one wire plus common) transmission line for their data signal. It used a 4-pin XLR connector, wired as follows: shield or common on pin 1, data (minus) on pin 2, rack overtemp sense on pin 3, and no connection on pin 4. The original version was used with Celebrity consoles and PC398 dimmer decoder cards until about 1987. It carried level data for 512 dimmers in one continuous packet. The later version incorporated 16 x 32-dimmer blocks and a separate (optional) softpatch packet that would be transmitted any time the patch needed to be changed. PC458 decoder cards were required for this version. There was no battery backup in the racks for the patch data, so if the racks lost power the patch would be reset 1-to-1 when power was restored. All versions reserved FFh for a start code, so the maximum value that a channel can reach is FEh (decimal 254).
Interfacing Hints - Since most QD racks used PC399 receivers and single-ended the data signals, no more than 150' (50m) of cable should separate the protocol converter and the racks. Most installations were wired with shielded, paired cable suitable for carrying DMX512, so installing the converter near the racks should be easy. Only pins 1 and 2 should be connected at the protocol converter. A very few later racks had PC722 receivers which were compatible with differential signals, so as long as the converter can output differential ECmux there's no problem putting it in the control room. One problem with early PC399 receivers is the presence of 180-ohm resistors at locations R2, R8, R14 and R20 that attenuate the incoming signal to the point where the receiver functions poorly or not at all. If these resistors are in place, bypass them with wire jumpers.
History -- When Electronic Theatre Controls bought Lighting Methods Inc. in 1990, they acquired a great deal of dimming, control and interface technology. Included in the deal was LMI's digital control protocol, developed in the mid-1980s. Although much of LMI's product worked with 0-10 volt analog, the CH200 and Designer consoles, Fast Patch and RD digital dimmers were designed around the digital protocol. ETC products designed for compatibility with ETC/LMI included the Concept 500, and early Expression, Impression, and Insight series consoles. Software versions from 2.0 on were exclusively DMX512-compliant. Idea and Vision consoles supported several different protocols, ETC/LMI among them.
Details - ETC/LMI is a synchronous protocol utilizing two wire pairs. One pair is used for dimmer data and the other carries a sync signal. A 4-pin XLR connector is used for the signal lines, and signal common is ground-referenced at each end of the transmission line. LMI's pinout was data+ on pin 1, data- on pin 2, clock+ on pin 3 and clock- on pin 4. ETC consoles generally swapped the functions on pins 1 and 2. Data rate is 250 Kbaud. The protocol was originally designed to handle 144 dimmers, but ETC expanded its capacity to 1000 or more with the addition of softpatch functionality.
Interfacing Hints - ETC is the only company that supports ETC/LMI in any current product. The Response 2212 converter will accept the protocol as an input but only 24 LMI dimmers can be controlled from its output. If you have the RD series dimmers, your best bet is to purchase a new 2031B receiver card from ETC that's programmed to accept DMX512, then replace the rack's 4-pin XLR with a correctly wired 5-pin.
History -- Kliegl Bros. introduced their new digital control protocol along with the popular K96 fully digital dimmer rack system and the Command Performance console in 1981. The protocol was also used later with the Entertainer and Performer 3 and 4 consoles, and K100 dimmer racks. As conceived, K96 was a powerful protocol that incorporated data compression, high level commands and dimmer talkback features, although these advanced features were generally not used. It also carried softpatch data for storage in the rack processors.
Details - K96 runs at 83.3 Kbaud with 7-bit resolution. The protocol handles up to 512 channel levels and provides softpatching for thousands of dimmers. The electrical interface is RS422 with one pair used for control and the other for talkback. The Entertainer console is the only one that used the talkback feature. Softpatch data is stored in battery backed RAM at the rack processors; if the data is lost there will be no patch and the dimmers won't respond to channel levels on the incoming data line.
Entertainer and P-3 consoles had a 7-pin Viking connector on the back with the following pinout: pins 1-3 common, pin 4 talkback-, pin 5 talkback+, pin 6 data-. and pin 7 data+. P-4 consoles used a DB9 with common on pins 1 and 2, data+ on pin 3, and data- on pin 4. Wall plates generally had a 5-pin XLR where the shield was on pin 3, the data pair on pins 1 and 2, and talkback on pins 4 and 5. If in doubt, you can usually go by the wire colors: the red/black pair are data+ and data- respectively, and the white/black pair are talkback+/-.
Interfacing Hints - If you're buying a protocol converter to allow your new DMX console to talk to your old K96 or K100 rack, make sure that it is capable of sending a 1-to-1 patch to the rack. Otherwise the only device able to perform this function is your old Kliegl console. It's good practice to replace the RAM backup batteries once very 3 years or so.
History - NSI developed the Microplex protocol in the 1980s to fill an important market niche: an inexpensive method of getting multiplexed control signals from consoles to dimmer packs at the low end of the price scale. Coincidentally, they use a 2-wire scheme much like Strand's D54, that is, dimmer levels and sync signals on one conductor and common on the other. NSI's design, however, carries far fewer channels. On the upside, the signal characteristics are forgiving enough to permit the use of microphone cables. And small consoles can be powered over the data link. Leprecon and Lightronics have both adopted their own 128-dimmer versions of Microplex (Lightronics calls theirs LMX-128). All three of these companies still manufacture equipment that uses this protocol, although their higher-end products work with DMX512.
Details - There are two basic Microplex variants: NSI's version normally supports 64 dimmers, but in certain cases does 96; the Leprecon and Lightronics versions support 128 dimmers. They all use 3-pin XLRs wired as follows: common on pin 1, console power on pin 2, and signal on pin 3. The mux control signal is 0-10 volts.
Interfacing Hints - The 3 companies supporting this protocol seem to agree on almost everything but basic signal timing parameters, making interoperability a bit dicey. It's best to contact the factory for specific application advice. NSI, Lightronics and Gray Interfaces all make DMX to Microplex converters.
History - Teatronics introduced their own analog multiplex protocol in 1981. It first appeared on the Director lighting consoles, and was used later on the Producer series boards. The only dimmers that received the Tmux protocol were the first generation of Genesis 6 and 12-packs. Interestingly, Teatronics redesigned their products to be AMX192-compatible before USITT decided to standardize that protocol. Factory support for existing Tmux products can sought at teatronics.com.
Details - Tmux took a slightly different approach to analog multiplexing than the others. Analog was transmitted as a balanced, low impedance signal on a pair of wires, and the synchronizing clock was a high impedance signal on one conductor paired with the signal common. 5-pin XLRs were used: common on pin 1, analog+ on pin 2, clock on pin 3, analog- on pin 4 and no connect on pin 5. By coincidence, this arrangement made it easy to accept AMX192 on the same port.
Interfacing Hints - No one makes any interfaces for the Tmux protocol. If you want to convert your old Teatronics dimmers to accept DMX512, your only option is to purchase a DMX D/A and drive the dimmers from the packs' analog inputs.
Acknowledgements: Steve Carlson, High Speed Design; Milton Davis, Strand Lighting; Doug Fleenor, Doug Fleenor Design; David North, Electronic Theatre Controls; Tom Young, J.R. Clancy