Redundant Operating Characteristics - Steady State Operations
156 HC900 Process Controller Installation and User Guide Revision 19
06/14
Figure 83 – Modes of operation on RSM
RUN Mode (Locked)
In the Run mode, the controller performs all control and communication tasks needed for steady-state
operation. On-line configuration edits and configuration changes are inhibited.
RUN/PROGRAM Mode (Unlocked)
In the Run/Program mode, steady-state tasks are executed and on-line configuration edits are permitted.
Configuration changes made in this mode are retained in both RAM and Flash memory in the controller.
PROGRAM Mode (Locked)
In the program mode, all outputs are turned OFF, function blocks do not execute and configuration changes
are permitted. Exiting the Program Mode performs a cold-start, which clears all timers, counters, totalizers
and other function blocks with residual data. Function blocks are initialized to their initial state with no
reference to previous history. Exiting the Program mode updates the RAM and Flash memory of the
controller with the most recent configuration data.
Steady State Operations
• Lead Controller issues polls to I/O Racks for inputs
• Both Lead and Reserve read I/O responses from I/O Racks
• Lead and Reserve both execute function blocks in the control strategy
• Only the Lead Controller writes physical outputs to the I/O Racks
• Lead Controller responds to communication messages from host devices on the Supervisory Network
and RS-485 interfaces
• Lead Controller handles communications with HC900 peers
• Lead Controller handles communications with Modbus RTU slave devices
• Lead and Reserve exchange system status data to determine conditions for failover.
• I/O Scanners relay system status data between each Controller to determine conditions for failover
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