Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules - Manual (Page 51)

Rockwell Automation Publication 1756-UM058G-EN-P - November 2012 51
Common Module Features Chapter 3
Data Transfer on Either Cyclic Time or Change of State
Digital input modules always send data at the RPI, but they send data at a change
of state only if the COS feature is enabled. COS is more efficient than RPI
because it multicasts data only when a change occurs.
The table describes the two ways a module sends data to the owner-controller.
Set RPI
The Connection tab on the Module Properties dialog box lets you enter an RPI.
The RPI guarantees the slowest rate at which data is multicast.
The module’s actual data transfer rate may be faster than the RPI setting. But, the
RPI provides a defined, maximum period of time when data is transferred to the
owner-controller.
Follow these steps to set an RPI value.
1. On the Module Properties dialog box, click the Connection tab.
2. In the Requested Packet Interval (RPI) field, enter an RPI value.
3. Click OK.
Method Description
RPI A user-defined rate at which the module updates the information sent to its owner-controller.
This is also known as Cyclic Data Transfer.
COS Configurable feature that, when enabled, instructs the module to update its owner-controller
with new data whenever a specified input point transitions from On to Off and Off to On. The data
will be sent at the RPI rate when there is no change of state. By default, this setting is always
enabled for input modules.