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DMX512 is a serial protocol that is commonly used to control stage lighting and effects. It was originally intended as a standardized method for controlling light dimmers. It soon became the primary method for linking controllers, a lighting console for example, to dimmers and special effect devices such as fog machines and intelligent lights.
A DMX512 network employs a multi-drop bus topology with nodes strung together in a daisy chain. A network consist of a single DMX512 controller, which is the master of the network and only transmitter, and one or more slave devices. Each slave device has an IN connector and usually an OUT or THRU connector, were as the controller only has an OUT connector. The controller's OUT connector is connected via a DMX512 cable to the first slave's IN connector. A second cable then links the OUT or THRU connector of the first slave to the IN connector of the next slave in the chain, and so on until all slaves are connected. The specification requires a terminator to be connected to the final OUT or THRU connector of the last slave on the daisy chain.
A DMX512 network is called a "DMX universe." The OUT connector on a DMX512 controller can control a single universe. Each universe operates up to 512 channels with each channel's parameter ranging between 0 and 255. A controller simply changes the values of these parameters.
For the DMX512 protocol, the controller transmits asynchronous serial data at 250 kbits/s. The data format is fixed at one start bit, eight data bits, and two stop bits. Each data frame consists of the following, a break, mark-after-break, slot 0 (Start Code) and up to 512 slots of channel data, each containing one byte. The break, which signals the end of one packet and the start of another, cause the slaves to start reception and also serves as a position reference for the data bytes within in the packet. The first slot, slot 0, is reserved for a start code that specifies the type of data in the packet.
The CCS C Compiler comes with a DMX512 driver, dmx.c, which can be used to develop code for either a DMX512 controller or a DMX512 slave device. When setup for a DMX512 controller the following functions are provided, DMXInit() to initialize the driver, DMXSetChannel() to set the specified channel to the specified value, DMXGetChannel() to get the current set value for the specified channel, and DMXCommit() to transmit the DMX512 channel data to the slave device. When setup for a DMX512 slave device the following functions are provided, DMXInit() to initialize the driver, DMXKbhit() to determine if new data as been received, and DMXGetd() to retrieve the DMX data.
In addition to the driver, the CCS C Compiler also provides the following two examples: ex_dmx_controller.c and ex_dma_slave.c, showing how to use the DMX512 driver to build code for a DMX512 controller and a DMX512 slave device.
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CCS is a leading worldwide supplier of embedded software development tools that enable companies to develop premium products based on Microchip PIC® MCU and dsPIC® DSC devices. Complete proven tool chains from CCS include a code optimizing C compiler, application specific hardware platforms and software development kits. CCS' products accelerate development of energy saving industrial automation, wireless and wired communication, automotive, medical device and consumer product applications. Established in 1992, CCS is a Microchip Premier 3rd Party Partner. For more information, please visit https://www.ccsinfo.com.
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