Spectrum Controls 1756-CTR8, User Manual

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Chapter 3: Operation Within the ControlLogix System 3-3
Owner’s Guide 0300199-01 Rev. D
When a module resides in the same chassis as the owner-controller, the following
two configuration parameters will affect how, and when, the input module
multicasts data:
•
Real Time Sample (RTS) configured via Real Time Sample tag.
• Requested Packet Interval (RPI) configured via I/O module properties.
This configurable parameter instructs the module to perform the following
operations:
1. Scan all of its input channels and store the data into on-board memory.
2. Multicast the updated channel data (as well as other status data) to the
backplane of the local chassis.
This configurable parameter also instructs the module to multicast its channel
and status data to the local chassis backplane.
The RPI instructs the module to multicast the
current contents of its on-board
memory when the RPI expires, (i.e., the module does not update its channels
prior to the multicast).
NOTE
IMPORTANT : The RPI value is set during the initial module
configuration using RSLogix 5000.
It is important to note that the module will reset the RPI timer each time an RTS
is performed. This operation dictates how and when the owner-controller in the
local chassis will receive updated channel data, depending on the values given to
these parameters. If the RTS value is less than, or equal, to the RPI, each
multicast of data from the module will have updated channel information. In
effect, the module is only multicasting at the RTS rate.
If the RTS value is greater than the RPI, the module will multicast at both the
RTS rate and the RPI rate. Their respective values will dictate how often the
owner-controller will receive data and how many multicasts from the module
contain updated channel data.