The Global_Control telegram consists of two bytes. It is sent by the class 1 master as a multicast to address 127 (0x7F) and SAP = 58 (0x3A). The SDN service is used for this purpose.
Global Control:
Control |
Group allocation |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
Control |
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0 |
0 |
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0 |
Reserved |
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x |
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Clear Data, signalling the operating state of the class 1 master |
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x |
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UNFREEZE |
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x |
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x |
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UNSYNC |
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x |
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7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
Group allocation |
---|---|---|---|---|---|---|---|---|
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x |
Group 1 |
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x |
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Group 2 |
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x |
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Group 3 |
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x |
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Group 4 |
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x |
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Group 5 |
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x |
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Group 6 |
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x |
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Group 7 |
x |
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Group 8 or isochronous clock |
If the class 1 master is working with an isochronous cycle, group 8 will have a fixed reservation for the clock telegram and can no longer be used freely .