Function blocks support modes with the relevant fields:
Target Mode - The mode that the block is trying to attain. When an operator sets the mode, it is the target mode that is being set.
Actual Mode - The current operating mode of the block.
Permitted - Those modes allowed as target modes. Write service prevents setting target mode to a non-permitted mode. Permitted mode is configurable by the user for each instance of each block, as defined by the supported mode.
Normal - The correct mode for most cases of plant operation.
Each block supports a subset of the following modes through the named set parameter, SHED_OPT:
RCas - Can be a permitted target mode. Remote cascade connection to setpoint. Setpoint is driven through RCAS_IN (the RCas input). The block algorithm determines block outputs.
ROut - Can be a permitted target mode. Remote cascade connection to output. The block output is driven through ROUT_IN (the ROut input).
Cas - Can be a permitted target mode. Cascade connection to setpoint. Setpoint is being driven through CAS_IN (the Cas input). The block algorithm determines block outputs.
Auto - Can be a permitted target mode. Setpoint is local to the block, (not being driven externally). The block algorithm determines block outputs.
Man - Can be a permitted target mode. Operator or logic external to the function block determines output.
IMan - Is never a permitted target mode. Original definition was Initialization Manipulation, which means that the block tracks downstream operation (typically another block that has an open cascade).
LO - Is never a permitted mode. Local Override or locked output. For a control block, the output tracks a specific input (the action triggered by a discrete track switch input). For an output block, failure action initiates.
OOS - Is always a permitted mode. The block is out of service.
Modes have priority. The above is in inverse priority order. Higher modes have lower priority.