Operating instructions

12 1892 1335 - Orion Radio Modem Operating Instructions - v2.9 / Aug 2009
Mode E - Externally-controlled Telemetry
This mode is used where the inputs and outputs at many Outstations are individually
interrogated and controlled by external SCADA equipment at a Base station. The Base unit
relinquishes most of its functions to the SCADA equipment, which controls polling,
input/output, acknowledgements, retries and alarm handling via Serial Port B. In order to do
this, it must use the message protocol described in Appendix B on page 75.
The Base unit provides no telemetry input/output, nor does it send alarm messages, but User
Data is available independently as for the other modes, on Serial Port A.
Outstations in Mode E behave as for Mode I, returning input information and obeying output
commands in response to polls, except that input information is never spontaneously
volunteered. Alarms, however, are spontaneously volunteered if they are set and the unit is
set to permit initiation of transmissions. The SCADA must acknowledge any alarm sent to it
to avoid raising a Comms Alarm at the Outstation. See page 16 for more details.
Unlike Mode I, where broadcast is a distinct configuration, the SCADA may broadcast
whenever it wishes. Outstations never acknowledge broadcast messages in any Orion
mode.
Figure 5 illustrates the one-to-many topology.
Figure 5 - One-to-many topology with external SCADA
The over-air protocol is fixed and used for both User Data and telemetry.