User's Manual

Chapter Three Configuration
Man_455U-D Rev 3.01 Page 45
The RS232 DTR signal can be configured to act as a disconnect signal. If so configured
(AT&D), the DTR signal will force a hang-up (DCD reset) if the host device resets the DTR
signal.
In single-connect Acknowledged mode, the host devices use AT commands to select
destination addresses to connect to. Normally the only configuration required is a unit
address.
3.8 Dual Redundant Standby
Two 455U-D units can be connected together in a hot-redundant-standby arrangement. One
unit configured as a Primary is normally active, and the Secondary unit is inactive. If the
Primary detects an internal fault or operating problem, then the Primary unit becomes inactive
and the Secondary becomes active.
Dual Redundant Standby mode is implemented in Firmware versions 3.00 and later.
The trigger conditions for a change-over are:
♦ Complete failure of the active 455U - power failure, CPU failure;
♦ Loss of radio communications - radio “comms-fail”;
♦ Fault detected by internal diagnostics - over-temperature, antenna fault (high SWR),
frequency failed-to-lock, or transmitter PTT timeout;
♦ Operator request via configuration.
To prevent change-over during short term transient fault conditions, the trigger condition
must be present for a time period before the change-
over occurs (“dual redundant delay time”, register
S11). If the primary unit changes over to the
secondary unit, the secondary unit remains as the
active unit until it detects a fault, or until it is forced
to change by manual configuration.
The inactive unit continues to operate, and can
receive messages via the radio and data ports.
However it is disabled from transmitting messages
on the radio and RS485 ports - it can transmit
messages on the RS232 port.
Both the primary and standby units should have the
same configuration except for the Redundancy
setting. The redundancy setting can be configured
from the ”DIO Redundancy” tab, which also displays
the current redundancy status.