Rockwell Automation 1756-IF4FXOF2F ControlLogix High-speed Analog I/O Module - Manual (Page 17)

Rockwell Automation Publication 1756-UM005B-EN-P - January 2013 17
High-speed Analog I/O Operation in the ControlLogix System Chapter 2
Direct Connections A direct connection is a real-time data transfer link between the controller and
the module 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.
If a controller has configuration data referencing a slot in the control system, the
controller periodically checks for the presence of a device there. When a device’s
presence is detected, the controller automatically sends the configuration data
and 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 appears 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 continuously 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. Relay ladder logic may be used to monitor this
data area to detect the module’s failures.