Rockwell Automation Publication 1756-UM058G-EN-P - November 2012 21
Digital I/O Operation in the ControlLogix System Chapter 2
Refer to the following general steps when configuring I/O modules.
1. Configure all I/O modules for a given controller by using
RSLogix 5000 software and download that information to the controller.
2. If the I/O configuration data references a scheduled connection to a
module in a remote chassis connected via the ControlNet network, run
RSNetWorx for ControlNet software to schedule the network.
3. After running RSNetWorx software, perform an online save of the
RSLogix 5000 project to make sure the configuration information that
RSNetWorx software sends to the controller is saved.
Internal Module Operation
ControlLogix I/O modules experience signal propagation delays that must be
accounted for during operation. Some of these delays are user-configurable, and
some are inherent to the module hardware.
For example, there is a small delay, typically less than 1 ms, between when a signal
is applied at the RTB of a ControlLogix input module and when a signal is sent
to the system over the backplane. This time reflects a filter time of 0 ms for a DC
input.
This section offers an explanation of the time limitations with ControlLogix I/O
modules.
Input Modules
As shown in the illustration below, ControlLogix input modules receive a signal
at the RTB and process it internally through hardware, filters, and an ASIC scan
before sending a signal to the backplane via the requested packet interval (RPI) or
at a Change of State (COS) occurrence. The RPI is a configured interval of time
that determines when a module’s data is sent to the controller.
You must run RSNetWorx for ControlNet software whenever a new I/O module
is added to a scheduled ControlNet chassis. When a module is permanently
removed from a remote chassis, we recommend that you run RSNetWorx for
ControlNet software to reschedule the network and optimize the allocation of
network bandwidth.
42701
Hardware Delay
Filter Delay
ASIC Delay
Signal Applied
at the RTB
Signal Sent to
the Backplane
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