Allen-Bradley 1756-DHRIO - Remote I;O Scanner Fault Notification

Publication 1756-UM514B-EN-P - February 2003
8-16 Using the 1756-DHRIO Module in Remote I/O Applications
Remote I/O Scanner
Fault Notification
A 1756-DHRIO 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 4 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
module has not been configured for a major fault to occur if
communication fails. In this case, the ControlLogix controller
repeatedly attempts to reestablish communications with the
1756-DHRIO module.
TIP
The update rate for the data exchange should be 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 communications if
the 1756-DHRIO module loses data flow from the
ControlLogix controller.