DiSEqC stands for Digital Satellite Equipment Control and is pronounced Die-Sec. It is a special communication protocol between a satellite receiver and a device that can be a multidish switch or a small dish antenna rotor. Developed by European satellite provider Eutelsat, it now acts as a standard agency for the protocol. It is usually used to control switches and motors and relies on a coaxial cable to transmit both bidirectional data or signals or power. It is touted to be more flexible than 13/18 V and 22 kHz tone or Toneburst/MiniDiSEqC techniques. Because one of its functions is to control bidirectional data, it is naturally compatible with actuators that are used to rotate the large C-band dishes when used with a DiSEqC positioned. And although its name suggests that it is used for digital systems, it has been used for fully analog or only partially digital-capable satellite receivers. There exist a number of DiSEqC variations that have different capabilities and functions. For instance, DiSEqC 1.0 allows switching between up to four satellite sources, whereas its counterpart, the DiSEqC 1.1, allows switching between up to 16 satellite sources. DiSEqC, in addition to allowing switching between up to 16 satellite sources, also aids in control of a simple horizontal-panning satellite motor. DiSEqC 2.0 adds bidirectional communications to DiSEqC 1.0. DiSEqC 2.1 and 2.2 do the same (adding bidirectional communication) to DiSEqC 1.1 and DiSEqC 1.2, respectively.
This is how DiSEqC works. The DiSEqC messages are transmitted as sequences of short busts of about 22 kHz tone that are modulated on the low noise block (LNB) power supply and are carried on the coax cable from the LNB input on the receiver, which is designated the master. The messages are made up of a number of digital bytes of eight bits each, with each of them occupying a specific time; the proportion of that time filled with the 22 kHz signal determines whether the bit concerned is 1 or 0. The initial byte is known as the framing byte, and the first five of these bytes follow the pattern “11100” so as to allow listening devices (designated slave) to synchronize with the signal. The sixth bit is set to zero in the event that the message is a command from the master. Likewise, it is set at 1 if the message is received from a slave. The seventh bit is set at 1 if a response is necessary and 0 if it is not. The last framing bits indicate whether the message is a retransmission of a message to which a reply has not been received.
The second byte indicates the group of devices the message is meant for. Actually, the first four bits signal the type of device (whether switch LNB or positioners and the like), and the rest of the bits give a clear indication of the particular device. In all cases, a value of zero means that the message is open to all. The command byte, on the other hand, gives direction to the listening devices, and this necessitates the transmission of a number of data bytes to pass on numbers that are relevant to the command.
For more information on DiSEqC read What is DiSEqC?