Spectrum Controls 1756-CTR8, User Manual

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3-2 Chapter 3: Operation Within the ControlLogix System
Owner’s Guide 0300199-01 Rev. D
Follow these general guidelines when configuring I/O modules:
1. Configure all I/O modules for a given controller using RSLogix 5000
and download that information to the controller.
2. If the I/O configuration data references a module in a remote chassis,
run RSNetWorx.
NOTE
Important: RSNetWorx must be run whenever a new module is added to a
networked chassis. When a module is permanently removed from a remote
chassis, we recommend that RSNetWorx be run to optimize the allocation
of network bandwidth.
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.
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. 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.
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
any module failures.
In traditional I/O systems, controllers poll input modules to obtain their input
status. Analog input modules in the ControlLogix system are not polled by a
controller once a connection is established. The modules multicast their data
periodically. Multicast frequency depends on the options chosen during
configuration and where in the control system that input module physically
resides. An input module’s communication, or multicasting, behavior varies
depending upon whether it operates in the local chassis or in a remote chassis.
The following sections detail the differences in data transfers between these set-
ups.