Rockwell Automation 1756-DHRIO_DHRIOXT ControlLogix Data Highway Plus-Remote I/O Communication Interface Module - Manual (Page 108)

108 Rockwell Automation Publication 1756-UM514C-EN-P - June 2014
Chapter 9 Using the 1756-DHRIO and 1756-DHRIOXT Modules in Remote I/O Applications
Configure the Data Exchange
Rate Between the Modules
and a Controller The following sections describe the process of setting the Requested Packet
Interval (RPI) for data exchanges between the 1756-DHRIO or
1756-DHRIOXT module and the ControlLogix controller. An RPI must be set
for the remote I/O scanner status connection and each adapter connection.
Requested Packet Interval (RPI)
This interval specifies the rate at which the 1756-DHRIO or 1756-DHRIOXT
module and the ControlLogix controller produce data. The time ranges from
3…750 ms and is sent to the module with all other configuration parameters.
When the specified time frame elapses, the 1756-DHRIO module and the
ControlLogix controller produce data for each other.
RIO Scanner Status Update Rate with the Module in a Local Chassis
When a module resides in the same chassis as the owner controller, the RPI
affects how and when the module produces link status and consumes the
controller status. The rate at which the status is exchanged is equal to the RPI.
RIO Scanner Status Update Rate with the Module in a Remote Chassis
If a module physically resides in a chassis other than that of its owner-controller
(that is a remote chassis connected via ControlNet), the rate at which the status is
exchanged is equal to the RPI + 2 x [Network Update Time (NUT)].
Configure the Baud Rate
The rate of I/O data exchange is directly related to the configured remote I/O
scanner baud rate. Your 1756-DHRIO and 1756-DHRIOXT modules allow the
following baud rates:
• 57.6Kbaud
• 115.2Kbaud
• 230.4Kbaud
The remote I/O scanner scan each remote I/O adapter at the following rates:
• 8ms/adapter @ 57.6Kbaud
• 5ms/adapter @ 115.2Kbaud
• 3ms/adapter @ 230.4Kbaud
TIP To maximize notification of the module status, we recommend setting the
1756-DHRIO and 1756-DHRIOXT modules’ RPI value equal to the RPI used
in the adapter connections.