166 HC900 Process & Safety Controller User and Installation Manual Revision 6
21 April 2017
Figure 87 – 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. SIL application must
operate in this position. SIL requirements may not occur in other operational modes. This RUN-locked
mode is the Safety mode for Safety controllers and the proper normal operational mode for all controllers.
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.
The Run/Program mode should be used only when changes are anticipated. The Run-Locked mode is the
preferred operational mode to prevent any unintentional changes.
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
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