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17.12 LAN alarm management
17.12.1 Preliminary considerations
The network may be disconnected because of one of the following instances:
•
fault in the LAN board of the controller (integrated into the board: in this case the entire board must be replaced);
•
LAN board connection cable disconnected;
•
Unit or controller power feed disconnected;
•
Cable broken in between the two units.
The options are two:
•
One or more units are no longer visible.
•
The network is broken into one (or more) sections.
Every unit constantly receives status information (namely, visibility or invisibility) of all other units that should be connected to
the network (based on the number of LAN units set through the user terminal). Every unit is capable of detecting any
disconnection.
17.12.2 Management algorithm
The algorithm generally involves the following:
•
The signal is always provided by the unit that is disconnected (isolated) from all the others, provided it is powered.
•
If the highest visible addressing unit coincides with the last one planned for the network, the signal is provided by the
unit that sees itself as the one with the lowest address of the visible ones.
•
If the highest visible addressing unit does not coincide with the last one planned by the network, the signal is provided
by the unit that sees itself as the one with the highest address of the visible ones.
•
If the highest visible unit is not the one planned to be last and the lowest one is not 1 (that is, the one planned to be
first), the unit in question is inside an internal LAN section and the signal is provided by the highest and the lowest units
of that section.
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