Figure 31: Automatic Role Switch (Aut_Sw) Function Block - GE PACSystems RX3i Application Manual

Chapter 5. PLC Hardware Configuration (Primary PLC)
Automatic Role Switch
Zoom into the DBUS block to display the Automatic Role Switch (AUT_SW) function block. This function block
allows the user to transfer control from the current Active PLC to the current Backup PLC in the event that a
GCG associated with the Active PLC fails.
While the function block is enabled, it will evaluate the Genius combined status bits that are received from the
Active PLC and compare them with the Genius combined status bits in the Backup PLC. The comparison is
performed within the Serial Bus Address range of 01..29. If any bit in the Backup PLC is ON while it's
comparable bit in the Active PLC is OFF, a corresponding timer will be enabled. If the timer expires, a service
request will be issued to effect a role switch.
EN_AUTO This Boolean reference determines if automatic switching is active in the Backup PLC.
SP The timer preset that is applied to the bit comparisons.
CSB This should not be changed. (It is the reference to the Combined Status Bits).
NUM This should not be changed. (It is the reference to the Bus Number [0..15]).
30

Figure 31: Automatic Role Switch (AUT_SW) Function Block

PACSystems* RX3i Genius Dual Bus Application Guide GFK-2928