Chapter Two
Operation
MAN_105G_1.5
Page
20
2.6
Radio Comms Failure
The 105G has an internal "communications failure" (comms fail) status for each I/O point in
its database. There is also a comms fail status for each module with direct communications -
see 2.5.1 above.
For I/O registers which are mapped to a remote output or another 105G, the comms fail status
is set if the 105G does not receive an acknowledgement for a message being sent to that
remote output. The comms fail status resets when a successful transmission occurs.
For I/O registers which have been mapped , from a remote input or another 105G, a comms
fail time period may be configured. If a radio message for this I/O register has not been
received within this time, then this registers comms fail status is set. The comms fail status
will reset when a message is received for this register. If the comms fail time is configured as
zero, then the comms fail status will never be activated.
The communications failure status is bit 15 of the status register for each I/O point. If the
host device reads a register as a digital or binary value, then the 105G returns bit 15 of the
register (0 or 1) - this is the comms fail bit of a status register.
It is important to use the comms fail status in the overall system design, as any system can
fail.
The 105G also provides an additional comms failure feature to stop the 105G transmitting
output messages to an individual remote address if the 105G already knows that this remote
address is in communication failure. This prevents the 105G from congesting the radio
channel with a lot of unnecessary transmissions (and re-transmissions). This function is
called "Don’t Send if In Comm Fail" and is configurable by the user for each individual
remote address. The 105G retains a "remote address comms fail" status for the remote
addresses configured for this function. If any output with this remote address goes into
communications failure, then the remote address comms fail status is set ("on" or 1) - every
time an input with this remote address receives a radio message, then the remote address
comms fail status is reset ("off" or 0). While the remote address comms fail status is set, the
105G disables any output messages being sent to this remote address.
When this feature is configured, all output transmissions are stopped if communications with
a remote module fails for a short period. They will start again when an input message from
this module is received. If the 105G determines that a output message should be sent to an
output which is disabled because of this feature, then the output message will not be sent and
the comms fail status of that output is set ("on" or 1).
If it is desired to use this function with a remote 105U module, but there are no inputs from
this module being used, then it is easy to configure an unused input or an internal input (mains
fail or low battery voltage etc). It is the comms fail status for the input, which is used, not the
input itself.
2.6.1
Monitoring Communications Failure
The host device can monitor the communications status of an I/O point by reading the status
register for this point as a binary/discrete register. Modbus, and many other protocols, will
convert a 16 bit register value to a binary/discrete value by returning the most significant bit -
for the status register, this corresponds to the comms status bit.
