Rockwell Automation Publication 1756-UM013B-EN-P - October 2019 33
Digital Safety I/O Module Operation in a Control System Chapter 1
Local Safety Output Modules
Local safety output modules receive output data from a controller and send data
to the controller. The data exchange occurs over the system backplane.
Controller to Local Output Module Data Transmission
The controller broadcasts data to its local backplane at the RPI.
The safety outputs are sent to the safety output module at the end of safety task.
The safety output RPI is set by the safety task period.
These events occur when the controller sends data to a local safety output
I/O module.
1. The controller sends data to system backplane at the RPI.
2. The local output module receives the data from the system backplane and
behaves as dictated by its configuration.
Local Output Module to Controller Data Transmission
When a local safety output module receives new data and the requested data
value is present on the RTB, the output module sends output readback status to
the controller. The data value corresponds to the signal present at its terminals.
In addition to the output readback, the output module sends other data to the
controller at the RPI. For example, the module alerts the controller if a short
circuit condition exists on the module.
The following events occur when a local safety output module sends data to the
controller at the RPI.
1. The module sends the data to the system backplane.
2. The controller receives the data immediately.
Remote Safety Output Modules
Remote safety output modules receive output data from a controller and send
data to the controller. The data exchange occurs over an EtherNet/IP network.
Controller to Remote Output Module Data Transmission
The controller broadcasts data to its local backplane at the RPI. The owner-
controller does not depend on the program scan to complete to send data.
IMPORTANT You cannot use Immediate Output (IOT) instructions in safety programs.
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