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Listen Only Mode
Operating Mode Selections
For more information on guidelines for specifying RPI rates, see the
Logix 5000 Controllers Design Considerations Reference Manual, publication
1756-RM094.
Any controller in the system can listen to the data from an ASCII module. An
owner-controller exchanges data with the ASCII module.
Other controllers can use a Listen Only connection with the module. In this
case, the 'listening' controller can only listen to input data or 'echoed' output
data. The listening controller does not own the module configuration or
exchange other data with the module.
During the I/O configuration process, you can specify a Listen Only
connection. For more information on Connection options, see
Definition on page
17.
IMPORTANT Remember the following:
• If a controller attempts to use a Listen Only connection to a module but the
owner-controller connection uses the Unicast option, the attempt at a Listen
Only connection fails.
The 'Listen Only' controller receives data from the module as long as a
connection between an owner-controller and module is maintained.
• If the connection between an owner-controller and the module is broken, the
module stops sending data and connections to all 'listening controllers' are
also broken.
The ASCII module has several different operating modes, some of which are
available only in certain combinations. Major options are summarized below,
with additional details provided in
Transmit Handshake and Transmit Immediate Option
This option defines when the ASCII module transmits data out of its
serial port.
With Transmit Handshake active (default), the ASCII modules keys on the
second byte (Transmit Record Number) of the poll command or explicit
message to determine whether the consumed data from controller is to be
transmitted out the serial port. While this Transmit Record Number is static,
the module does not transmit the command data. Upon sensing a change in
value of the Transmit Record Number byte, the module transmits the data. It
initiates one serial transmission for each change in the Transmit Record
Number value, regardless of the data string value.
In Transmit Immediate mode, the ASCII module ignores the Transmit Record
Number byte value and initiates a new serial port transmission with each
message that is received from the controller.
Carefully consider when you select this option for I/O messaging. See
POINT I/O Parameters on page 25
Rockwell Automation Publication 1734-UM009C-EN-P - August 2022
Chapter 1
Overview of the POINT I/O ASCII Modules
Chapter
2.
for details.
Module
11
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