Lan Alarm Management; Preliminary Considerations; Management Algorithm; Examples - Mitsubishi Electric s-MEXT-G00 006 Technical Manual

TM_s-MEXT_ME28relC_00_12_19_EN
20.8

LAN ALARM MANAGEMENT

20.8.1

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.
20.8.2

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.
20.8.3

Examples

The following examples refer to a LAN with 8 units connected.
Example 1
•
Situation: Unit 4 disconnected from all the others.
•
Units signalling the LAN disconnected alarm: 1 and 4 (if powered and working).
Example 2
•
Situation: Unit 1 disconnected from all the others.
•
Units signalling the LAN disconnected alarm: 1 (if powered and working) and 2.
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