Rockwell Automation 1756-CFM ControlLogix Configurable Flowmeter Module - Manual (Page 21)

21 Rockwell Automation Publication 1756-UM010B-EN-P - December 2011
Configurable Flowmeter Operation in the ControlLogix System 21
Connections
Logix controllers make connections to 1756-CFM modules to exchange data.
The controller can make either of the following connections to a 1756-CFM
module:
 Direct Connections - Only one controller can make this connection to a
CFM module.
 Listen-Only Connections - Multiple controllers can make this
connection to a CFM module simultaneously.
Direct Connections
A direct connection is a real-time data transfer link between the controller
and the device that occupies the slot that the configuration data references.
When module configuration data is downloaded to an owner-controller, the
controller attempts to establish a direct connection to each of the modules
referenced by the data. One of the following events occurs:
 If the data is appropriate to the module found in the slot, a connection
is made and operation begins.
 If the configuration data is not appropriate, the data is rejected and an
error message displays in the software. In this case, the configuration
data can be inappropriate for any of a number of reasons. For example, a
module’s configuration data may be appropriate except for a mismatch
in electronic keying that prevents normal operation.
The controller maintains and monitors its connection with a module. Any
break in the connection, such as removal of the module from the chassis while
under power, causes the controller to set fault status bits in the data area
associated with the module. The RSLogix 5000 software may monitor this data
area to announce the modules’ failures.
IMPORTANT
The typical Logix controller can make and maintain up to
250 connections. Each 1756-CFM module requires 1
connection.