3.2 DMX Communications
In the world of digital communications, information is sent using precise electrical voltage pulses. A positive voltage pulse represents a 1. A zero voltage pulse (or no voltage) represents a 0. Systems using 1’s and 0’s to encode information are called binary systems.
Each pulse in a digital signal is called a binary digit, or bit. A bit can only have one of two values, 1 or 0. A grouping of eight bits, called a byte, is used to carry one piece of information. This ‘information’ is simply a value ranging from 0 to 255.
The most common method of transmitting digital signals is to send data one bit at a time in one direction over one wire. Since each bit is transmitted in series, this method is known as Serial Communication. In its simplest form, Serial Communication requires one data wire for transmission and one common reference (or ground) wire.
There are two types of Serial Communication:
•Synchronous
•Asynchronous
In Synchronous data transmission, data is sent as a group of characters in a single stream of bits known as a bit- stream. For this method to work, timing devices at both ends must be in perfect synchronization, requiring precision equipment at a higher cost.
In Asynchronous data transmission, data is sent one byte at a time. Asynchronous devices do not require perfect synchronization, but their timing signals must be close (within about 5%). This method is relatively simple, and therefore inexpensive.
There are many standards for Serial Communications, each having its own advantages and disadvantages. Communications standards generally fall into two broad categories:
•
•Differential (balanced)
The
The DMX 512 protocol is based on the
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