DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

Fikri — Thu, 30 Oct 2025 01:53:22 GMT

Thank you bro, i just read all of the above, it realy opened my new understanding of DMX512 protocol, big thank

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

neilk — Thu, 13 May 2021 13:44:52 GMT

Hi shabaz

I've only just read the original blog post and found it fascinating!

As a student in the late 60s, I got involved in theatre lighting, from ancient rheostat systems through to quite sophisticated thyristor based boards. I gave up my involvement with amateur dramatics in the mid 70s. Since then I've watched the increasing level of sophistication in lighting control systems and the introduction of LEDs and remote control pan and tilt.

I've often wondered about the underlying control protocols - now I know!

Thanks again for posting this

Neil

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

ansarirahim — Mon, 10 May 2021 02:31:07 GMT

[mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05]

Very well explained, it not only covers DMX512 but also UART LSB first concept.

If microcontroller doesn't have such support and bit banging also seems to be not feasible for achieving 4uS width ...and if we have SPI availability and set clock rate to 250000 Bits/s.

Can we not go with this SPI, ?

1. If we didn't connect clock signal-ignored it.

2. taken care of LSB First in the firmware.

3. 11 bits considered : 2Bytes sent

Is it possible or more things are required?

OR Bit Banging is enough for aurdino nano...?

thanks

Ansari

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

beacon_dave — Sat, 11 Aug 2018 09:44:24 GMT

[mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05] - This may be of interest, Microchip appear to have added DMX-512, DALI, & LIN protocol support to the UART in their newer PIC 8-bit microcontrollers.

DMX-512 using the UART with Protocol Support

http://ww1.microchip.com/downloads/en/AppNotes/TB3204-DMX-512-using-UART-90003204A.pdf

DMX Controller using the UART with protocol support module

https://mplabxpress.microchip.com/mplabcloud/example/details/517

DMX512 Receiver using PIC18FxxK42 with DMA

https://mplabxpress.microchip.com/mplabcloud/example/details/382

It looks like you can also use the Direct Memory Access module with this new UART to off-load even more tasks from the core processing.

Unfortunately Microchip don't appear to have added the same UART functionality to the likes of the AVR ATMEGA4809 as used in the new Arduino UNO WiFi.

For those interested in WS2812 pixel LEDs, then the PICs Configurable Logic Cell module may also be of interest.

Using the Configurable Logic Cell (CLC) to Interface a PIC16F1509 and WS2811 LED Driver

http://ww1.microchip.com/downloads/en/AppNotes/00001606A.pdf

8x32_NeoPixel_LED_PIC18FxxK42

https://mplabxpress.microchip.com/mplabcloud/example/details/378

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

genebren — Mon, 27 Nov 2017 22:28:20 GMT

This was a really nice article. Back in July, I brought on a new client who wanted me to build him a new animatronics controller based on DMX-512A. I had never heard of DMX so I did a quick bootstrap on the subject and got started. I did not take too much time to understand the basics, but it took way longer to fully understand that not all products out there followed the specification. I found that I had to be very flexible in how I interpreted the timing, especially the start-of-packet timing.

I have since completed that project and have moved on to a couple of related products and enhancements to the first one.

It is always nice to learn something new and even better to be able to build on what you learned.

Gene

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

mcb1 — Thu, 14 Sep 2017 06:55:53 GMT

Nice post [mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05]

I've had a dabble with the end products, but haven't got heavily involved in trying to understand the protocol.

A comment from a co-worker who spent some time with DMX equipment was it has become like the wild west with equipment and what responds correctly.

Mark

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

jc2048 — Fri, 25 Aug 2017 09:40:42 GMT

Nicely done - some useful information there. I found this section a bit ambiguous.

RS-485 is a method for connecting up different devices. It uses three wires; two carry signals in a balanced format, and the third is a 0V reference wire. Multiple devices can be connected to this wiring bus although in practice with DMX lighting only one device is connected at each end; a master and a slave.

Since lighting could involve many devices, it is possible to have two separate RS-485 connections per lighting device. One connection acts as a RS-485 slave from the controller, and the other connection acts as a RS-485 master for connecting to another lighting device in the daisy-chain.

I know what you meant, but a diagram would have helped to emphasise that the bus is multidrop, with the lamps 'T'-ed off of it (even though the 'T' is normally hidden inside between the 'in' and the 'out' connectors). As it stands, someone might intepret what you written as the fixture buffering the signal and then sending it on. It needs to be multidrop to allow for RDM (Remote Device Management) where the fixture can transmit data back to the desk/controller. You might also mention that strictly, to conform with the spec, the input should be isolated (to avoid problems with ground loops in a large scale installation) - obviously, for a personal project, you can just ignore that, but for a commercial product you'd need to work to the spec.

But the main point you're making, that DMX512 is a simple protocol that's easy to generate and decode, is spot on and hopefully you'll encourage some activity here in that area. (It's easy to generate because you're just throwing bytes at a UART and then slapping in a long break every once in a while. It's easy to decode because you just have to recognise the break, check the start code, and then count off received bytes until you get to the ones you want.)

If 'something in a tin box' wins for September, perhaps someone could have a go at 'DMX512 in a Baked Bean Can'.

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

14rhb — Thu, 24 Aug 2017 19:10:50 GMT

Shabaz,

A nice summary of this really useful protocol; thank you for your clear explainations.

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

beacon_dave — Thu, 24 Aug 2017 18:35:16 GMT

Nice write-up Shabaz.

Just a quick heads-up but the packet's first frame byte (AKA 'the start code'), is not always 0x00.

There is a list of known alternate start codes in use available on the Entertainment Services and Technology Association (ESTA) web site at:

http://tsp.esta.org/tsp/working_groups/CP/DMXAlternateCodes.php

People may want to ignore packets with start codes that are not 0x00 as it can send erratic movements to PTZ motors in moving fixtures.

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

DAB — Thu, 24 Aug 2017 18:34:19 GMT

Great post Shabaz.

Well done.

DAB