DiSEqC explanation

The DiSEqC system designed by EUTELSAT provides a method of controlling a wide range of equipment and accessories connected to the satellite receiver. The abbreviation DiSEqC means Digital Satellite Equipment Control.

A 22 kHz amplitude modulation is used to form DiSEqC data bits and messages and their transmission via a cable. In principle, logical1 data bit is represented by a 0.5 ms burst of a 22 kHz tone (of approx. 0.6 V amplitude) followed by a 1 ms pause, and a logical 0 data bit is represented by a 1 ms burst followed by a 0.5 ms pause.

The bits are grouped into bytes, each byte consists of 8 bits and one parity bit, and typical DiSEqC command string consists of 3 or 4 bytes. The first byte is the so-called Framing byte, the second is an Address byte, followed by the Command byte and, if need be, by a Data byte. The end of each command string is detected by a pause in the 22 kHz carrier.

DiSEqC commands are able to coexist on the same cable with the established voltage/tone switching signals (13/17 V, 0/22 kHz signalling) and with a Tone Burst command. This means that the satellite receiver can control both old LNBs and switches and new DiSEqC accessories at the same time.

The so-called Tone Burst command has been designed to be detected by a cheap analogue circuit, as an extension to the DiSEqC command set. 0 (or A) Tone Burst command is defined as a 12.5 ms burst of 22 kHz tone (unmodulated Tone Burst), 1(or B) is defined as a 12.5 burst of a 22 kHz amplitude modulated tone and is identical to eight repeated logical 1 DiSEqC data bits followed by one 0.5 ms burst of a 22 kHz tone.

There are different levels of implementation of the DiSEqC system. For satellite accessories DiSEqC 2.0 level has been developed, which enables two-way communication between a satellite receiver and accessories connected to the receiver.

The equivalent DiSEqC 2.0 command to voltage/tone switching signals and to Tone Burst command is Write N0 command. For this command, the Command byte is 38 h (in hexadecimal format), and the Data byte is Fx h, where x are four bits whose value can be from 0000 to 1111. In ascending order, the first bit defines the logical value for Option, for which there is no equivalent among voltage/tone switching signals, the second bit defines the logical value for Position (equivalent to Tone Burst command), the third bit defines the value for Polarization (equivalent to 13/17 V), and the last fourth bit defines the value for low or high band (equivalent to 0/22 kHz). The following table shows the relation between the DiSEqC Write N0 command and voltage/tone switching commands:

FunctionVoltage/tone switching commandWrite command data (38 h)
Low Band0 kHz1111 xxx0 b
High Band22 kHz1111 xxx1 b
Vertical Polarization13 V1111 xx0x b
Horizontal Polarization17 V1111 xx1x b
Position ATone Burst “0”1111 x0xx b
Position BTone Burst “1”1111 x1xx b
Option A1111 0xxx b
Option B1111 1xxx b

All EMP-Centauri switches support DiSEqC 2.0 commands, but they are also compatible with voltage/tone switching signals. If there is not a DiSEqC generator built in the satellite receiver connected to the switch, the switch is controlled by 13/17 V or 0/22 kHz or Tone Burst commands sent from the receiver. If the receiver with a DiSEqC generator is connected to the switch and the receiver sends a Write N0 command to the switch, the switch is controlled by the DiSEqC command.

The second byte of the DiSEqC Write N0 command, the so-called Address byte, corresponds to the address of the switch or the accessories connected to a satellite receiver. For EMP-Centauri DiSEqC switches, the Address byte is 14 h for switches with integrated power supply, and 15 h for the other switches.