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915U-2 Wireless I/O
A module can provide an output, which activates on communication failure to
another module. This can be used to provide an external alarm that there is a
system fault.
3.3.4 Indicating a Communications Problem
There are two ways to indication communications problems.
Fail-to-transmit alarm
The first method is to setup a communications indication on a register of your choice
when configuring a mapping. This can be done using an existing mapping (do not need
to setup a special comms mapping).
When entering a Block Write or Gather/Scatter Mapping you need to enter into the
"FailReg" field a register location that you wish to indicate a communications fail (As
mentioned previously this register can be a local DIO (Reg 1-8) or an internal register.
When ever the module tries to send this mapping and fails to get a response (Ack) it will
turn on the output.
The Comms Fail indication will clear on the next successful transmission of the
mapping.
This method will work with any number repeaters in the link; however it will only indicate
a failure to transmit if the mapping has the "ACK" field checked.
It will not give a Fail indication if the mappings are configured as Transmit only (do not
have the "Ack" ticked).
Fail-to-receive alarm
The second method is to set up a "Comms Link" indication on the receiving end using
normal Write Mappings on the transmitting end and the "Fail Safe Time" function on the
receiving end. Setup a comms mapping from an unused digital input (can be an internal
signal, i.e. Supply fail) and have it mapped to the output that will indicate the
communication status. The input will be updated at a given time interval (default will be
5 seconds) but select a time that will give a good indication of failure but not update so
much that it generates too many comms check messages, e.g. 30 seconds.
On the receiving end, configure a "Fail Safe Time" on the output that it being mapped to
of twice the update time e.g. 1 minute. Next, configure the Fail Safe State to be on
"ticked" which will turn on the output when it fails to be updated. Alternatively, you could
invert the mapping so the output was always on and then trigger the "Fail Safe State" to
go off when not updated.
This method will work with any number repeaters in the link.
You should use separate outputs to indicate "comms OK" of different remote modules.
3.3.5 Testing and Commissioning
We recommend that that the system is fully tested on the bench before installation. It is
much easier to find configuration problems on the bench when the modules are next to
each other as apposed to being miles apart.
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915U-2 Wireless I/O
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