Rockwell Automation 1756-RIO ControlLogix Remote I/O Communication Interface Module User Manual - Manual (Page 28)

28 Publication 1756-UM534B-EN-P - November 2010
Chapter 1 The 1756-RIO Module-Getting Started
Remote I/O Update Time
The remote update time is the time it takes the Remote I/O scanner to scan all
of the adapters in its I/O scan list.
The scan rate is the approximate time it takes to scan a 16-slot logical chassis
without block transfers. The number and sizes of block transfers can
significantly affect this time.
So, for example, if you have eight adapters on your network and your baud rate
is 230.4 K, your approximate remote I/O update time would be 8 (# of
adapters) * 3 ms (scan rate), or, 24 ms.
RPI
The Requested Packet Interval (RPI) specifies the rate at which the 1756-RIO
module and the ControlLogix controller exchange data to and from each
other. The allowable RPI’s range is from 2…750 ms, with a default of 20 ms.
When the specified time frame elapses, the 1756-RIO module and the
ControlLogix controller produce data for each other. All 1756-RIO input and
output tags update with the same RPI.
Select an RPI for your application. For most applications, a good rule of
thumb would be to set the RPI equal to one half of the remote I/O scan time.
Baud Rate Scan Rate
230.4 K 3 ms
115.2 K 5 ms
57.6 K 8 ms