Rockwell Automation 1756-DHRIO_DHRIOXT ControlLogix Data Highway Plus-Remote I/O Communication Interface Module - Manual (Page 110)

110 Rockwell Automation Publication 1756-UM514C-EN-P - June 2014
Chapter 9 Using the 1756-DHRIO and 1756-DHRIOXT Modules in Remote I/O Applications
Remote I/O Scanner Fault
Notification A 1756-DHRIO or 1756-DHRIOXT module using one of its channels for
remote I/O has a connection open between the module and its owner-controller.
The remote I/O scanner status is continually being exchanged over this
connection. This continuous data exchange is responsible for maintaining
module awareness in the system.
If at any time this continuous data exchange is interrupted for a time that is four
times the RPI, the ControlLogix controller drops the current remote I/O scanner
configuration and terminates communication with the adapters on the remote
I/O network. The channel configured for remote I/O scanner goes offline and
waits for new configuration data before beginning communication with the
remote I/O network.
The ControlLogix controller also performs one of the following scenarios:
• ControlLogix controller faults, if the 1756-DHRIO module has been
configured for a major fault to occur on the controller if communication
fails.
• ControlLogix controller does not fault, if the 1756-DHRIO or
1756-DHRIOXT module has not been configured for a major fault to
occur if communication fails. In this case, the ControlLogix controller
repeatedly attempts to reestablish communication with the
1756-DHRIO or 1756-DHRIOXT module.
TIP The update rate for the data exchange is set to go at the minimum RPI set
for the data flow between the ControlLogix controller and the remote I/O
adapters. This guarantees the scanner quickly terminates remote I/O
network communication if the 1756-DHRIO or 1756-DHRIOXT module loses
data flow from the ControlLogix controller.