Spectrum Controls 1756sc-OF8H Series A User Manual
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Chapter 3: Operation within the System 21
Modules in a Local
Chassis
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.
Real Time Sample (RTS)
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
Requested Packet
Interval (RPI)
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).
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. Note: Even
though data may be transferred at the RPI rate, the data will be
identical to the previous RTS data transfer. HART data can change.
Setting the RPI < 100 msec will allow you to see all changes.