Rockwell Automation 1756-IF4FXOF2F ControlLogix High-speed Analog I/O Module - Manual (Page 21)

Rockwell Automation Publication 1756-UM005B-EN-P - January 2013 21
High-speed Analog I/O Operation in the ControlLogix System Chapter 2
Module Output Operation
When specifying an RPI value for the high-speed analog I/O module, you define
when the controller broadcasts output data to the module. If the module resides
in the same chassis as the owner-controller, the module receives the data almost
immediately.
High-speed analog module outputs receive data from the owner-controller and
echo output data only at the period specified in the RPI. Data is not sent to the
module at the end of the controller’s program scan.
When a high-speed analog I/O module receives new data from an
owner-controller, the module multicasts or echoes the output data value that
corresponds to the analog signal applied to the output terminals
(1)
to the rest of
the control system at the next RPI or RTS, whichever occurs first. This feature,
called Output Data Echo.
Depending on the value of the RPI, with respect to the length of the controller
program scan, the module can receive and echo data multiple times during one
program scan.
Because it is not dependent on reaching the end of the program to send data, the
controller effectively allows the module’s output channels to change values
multiple times during a single program scan when the RPI is less than the
program scan length.
(1) Although the output value at the RTB screw terminal typically matches the output data echo value, it is not guaranteed to match.
The output data echo that is multicast to the rest of the control system represents the value the outputs were commanded to be.
Data Sent from Owner at the RPI
Owner-controller High-speed Analog I/O Module