User manual

Chapter 2 OPERATION
Page 25 ©February 2009
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 acknowledgment 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. . A reset of registers if in comms fail option is
available for values to reset back to 0.
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.