Using a PIC® Microcontroller for DMX512 Communication

AN1076 ® Using a PIC Microcontroller for DMX512 Communication place of auto-transformers, becoming quite popular, Author: Parthiv Pandya particularly the 0-10V analog consoles. Still, this Microchip Technology Inc. system had three major drawbacks: 1. It was prone to noise. 2. Dimming could be nonlinear depending onINTRODUCTION different kinds of lamps. DMX512 is a communication protocol used in most pro- 3. A separate control wire was required for each fessional theater lighting components such as dim- lamp. mers, scanners, moving lights, strobes, etc. This As computer technology became more cost effective, application note presents a solution to transmit and new digital consoles came to the market and with them receive the DMX512 communication protocol that can ® the need for a new standard that would allow microcontroller offer-be implemented using any PIC equipment from different manufacturers to ing a Universal Asynchronous Receiver Transmitter interoperate. (UART) module. In particular, the PIC18F24J10, a gen- eral purpose device, was used in the code examples The United States Institute of Theatre Technology, provided with this application note. It provides 1024 USITT, first developed the DMX512 protocol in 1986 as bytes of data memory, which allows the demonstration a standard digital interface between dimmers and con- code to store the data for the entire 512 channel buffer soles, later expanded and improved in 1990. The cur- (although this is not required for the typical application). rent version, known as DMX512-A, has also been Only an external RS-485 compatible transceiver is adopted as an American National Standards Institute required to complete the application schematic. (ANSI) standard (E1.11). The development of DMX512-A is currently managed by the Entertainment The DMX solution is provided in two parts: Services & Technology Association (ESTA). You can 1. DMX512 Transmitter: obtain (purchase) a copy of the protocol specifications This part will explain how to generate and transmit the web site or the www.ansi.orgfrom the www.esta.org DMX512 packets. This is divided into two subsections: web site. (a) how to generate and transmit the DMX512 packets ANATOMY OF THE DMX512 and PROTOCOL (b) a demo program that shows how to send commands to a DMX512 light dimming receiver. DMX512 (an acronym for Digital MultipleX), is 2. DMX512 Receiver: extremely simple, low cost and relatively robust. Due to these advantages DMX512 has gained a great popu- This part will explain how to receive the DMX512 larity. As the name suggests, it can support up to 512 packets. Once more, it is divided into two subsections: separate control channels/devices. It is a unidirectional (a) how to receive the data asynchronous serial transmission protocol which does not provide for any form of handshake betweenand receiver and transmitter, nor does it offer any form of (b) a demo program that sends the received data to the error checking, or correction mechanism. Hence, it is PWM module to control the brightness of a LED. not suitable for any safety critical application. Data is transmitted at 250k baud rate using a physical interface BACKGROUND compatible with the RS-485 transmission standard