User's Manual

Chapter Four Troubleshooting
Man_455U-D Rev 3.01 Page 63
4.8 Dual Redundancy
Two modems can be setup to act as a dual-redundant pair. If one modem fails, the second
modem can take over the communications task. One of the modems is designated the Primary
modem, and the other is designated the secondary.
Redundancy is configured via the AT#O command. #O3 configures the primary modem and
#O4 configures the secondary modem.
In addition, one of the two modems will be the currently active modem. This is normally the
primary modem, unless the primary modem detects a fault, in which case the secondary
modem becomes active.
To check the state of the Dual redundant system, you can:
• Observe the DIO LEDs on the two modules. These LEDs should be flashing together.
Refer to the following table to diagnose the flashing LEDs.
LED Sequence Redundancy Status
1½ seconds on, ½ second off. Normal operation. Primary is active, Secondary is
inactive but functional
1 second on, 1 second off Secondary Fault. Primary is active, Secondary is
inactive and has a fault
½ second on, 2 seconds off Secondary is active, Primary is inactive and has a fault
Always On Hardware fault on I/O Circuit or module fault -
disconnect wire to determine which module is
functional.
• Use the configuration port to read the status of S-Register S-33 to check the dual
redundancy status.
S33 Value Dual Redundant State
2 Active Primary
3 Active Secondary
4 Active Primary – no secondary detected
5 Inactive Primary
6 Inactive Secondary