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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:
| Function |
Voltage/tone switching command |
Write command data (38 h) |
| Low Band |
0 kHz |
1111 xxx0 b |
| High Band |
22 kHz |
1111 xxx1 b |
| Vertical Polarization |
13 V |
1111 xx0x b |
| Horizontal Polarization |
17 V |
1111 xx1x b |
| Position A |
Tone Burst "0" |
1111 x0xx b |
| Position B |
Tone Burst "1" |
1111 x1xx b |
| Option A |
- |
1111 0xxx b |
| Option B |
- |
1111 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.
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