I find it interesting that there is no clock pulse for which to synchronise the data to.
DMX is based on Asynchronous data transmission, data is sent one byte at a time.
Asynchronous devices do not require perfect synchronization and one device functions as the master (the DMX controller) on a network, while the rest function as Receivers (dimmers, intelligent fixtures, etc.). Only the master transmits over the
network, and all Receivers receive the same data (512 channels).
Devices are connected in a daisy-chain fashion, from the controller to device #1, then device #1 to device #2, and
DMX 512 data is transmitted at 250 kiloHertz (kHz), meaning that 250,000 1’s and 0’s (at a maximum) can be
sent each second. Each bit is measured in 4 microsecond (μs) intervals. In order for the receiving device to
correctly interpret the data, it must be sent in a particular sequence. A single transmission (DMX Packet)
includes synchronizing elements and channel data for up to 512 channels.
dmx protocol2.jpg [ 10.12 KiB | Viewed 1255 times ]
How does each piece of equipment know which channel it is?.
On each Receiver there are 9 switches which are then set by the user using Binary Coding, example: if switch one and three was set ON then this will set the Receiver to the Binary Code of 5.. So then the Receiver will then start to interpret the data on channel FIVE..
At this point I will also point out that some Receiving devices (with intelligent fixtures) use more than ONE channel, Depending on the Functions the unit has.
a Standard unit then uses this standard:
• Channel 1: Pan
• Channel 2: Tilt
• Channel 3: Color
• Channel 4: Gobo
When the devices are connected in a daisy-chain fashion, the amount of channels the device uses as to be noted and then set accordingly on the next device in the daisy chain so that two devices do not share the same channel.