Setting The Rate Of Data Exchange Between The Logix5550 And The 1756-Dhrio Module; Requested Packet Interval (Rpi); Rio Scanner Status Update Rate With The 1756-Dhrio In A Local Chassis; Rio Scanner Status Update Rate With The 1756-Dhrio Module In A Remote Chassis - Allen-Bradley ControlLogix User Manual

10-4 Remote I/O Operation
Setting the Rate of Data Exchange
Between the Logix5550 and the
1756-DHRIO Module
Publication 1756-6.5.14 - August 1998
Important: Each choice provides a way of determining what type of
adapter is present on the RIO network. They all behave
the same in the ControlLogix system. When online, the
1756-DHRIO module cannot tell which specific adapter
is connected to the RIO network.
The adapter output data sent by the Logix5550 is consumed by the
1756-DHRIO module on the connection created when you add
remote I/O devices in RSLogix 5000.
The output data is produced by the owner-controller at the RPI and is
not tied to the scan time of the controller's program. How often the
output data is sent by the RIO scanner to the RIO adapters depends
upon the number of adapters on the channel and the baud rate used.
The rack input data received in the adapter response is produced by
the 1756-DHRIO module immediately after the RIO adapter response
is received. The owner-controller receives the data directly into the
data buffer created by the software. The frequency at which the input
data is produced depends upon the number of adapters on the channel
and the baud rate used.
The following sections describe the process of setting the Requested
Packet Interval (RPI) for data exchanges between the Logix5550 and
the 1756-DHRIO module. An RPI must be set for both 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 module and
the Logix5550 produce data. The time ranges from 3mS to 750mS
and is sent to the module with all other configuration parameters.
When the specified timeframe elapses, the 1756-DHRIO module and
the Logix5550 will produce data for each other.
RIO Scanner Status Update Rate With the 1756-DHRIO 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 the status is exchanged at is equal to the RPI.
RIO Scanner Status Update Rate With the 1756-DHRIO Module in
a Remote Chassis
If a module physically resides in a chassis other than where its owner-
controller is (i.e. a remote chassis connected via ControlNet), the rate
the status is exchanged at is equal to the RPI + 2 x [Network Update
Time (NUT)].