9.3 Functioning of PIOMB
The PIOMB function block executes as an independent block at the base period of the CEE, which contains the
PIOMB function block.
When the PIOMB is in an "ACTIVE" execution state, it performs the following actions.
Connects to the DSB on load and receives data when active.
If the PDC is an input type PDC, performs input module processing.
If the PDC is an output type PDC, performs output module processing.
Connection and status processing
When a PIOMB is loaded, the connection status of the PIOMB with the PDC is monitored and the connection
status is displayed in the Module Configuration tab of the PIOMB block.
The following are the possible connection statuses.
Connected - The PIOMB is able to connect to the PDC with which it is associated.
NotConnected - The PIOMB is unable to connect to the PDC with which it is associated.
ConfigError - The PIOMB association with the PDC has runtime errors.
If the communication path is not intact, the PIOMB performs the following:
Generates the Communication Error notification.
Sets input data to fail-safe values.
Sets output data to back initialize.
Input module processing
If the PDC type is an input type and the communication path is intact, the PIOMB performs the following:
Receives the most recent input data for the device from the PGM.
Stores the input data and the status in the function block parameters and makes it available to the channels.
Output module processing
If the PDC type is an output type and the communication path is intact, the PIOMB performs the following:
Receives and stores the read-back values and the status in the function block.
Stores the output values that are to be sent to PGM in the communication layers of the devices.
Clamping of output process values
The PIOMB clamps the process data in the following two scenarios.
If the process value to be passed between the PIOMB and the DSB exceeds the values supported by the
configured channel data type. In such a scenario, the process value will be clamped to the maximum or the
minimum value supported by the channel data type.
The analog output value will be clamped to match the channel data type. This clamping will occur only after
the value is scaled.
Scaling of process data
The PIOMB handles the process value conversion between raw and percentage. When a PIOMB is associated
with a PDC, the channel high range and the channel low range values of each channel is made available to the
PIOMB. The channel low range is equivalent to 0% and the channel high range is 100% of the process value.
9 PROFIBUS I/O MODULE (PIOMB) FUNCTION BLOCK