PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 6
GFK-2222AK October 2019
Serial I/O, SNP & RTU Protocols 192
The maximum number of permanent datagrams that can be established is 32. When this
limit is reached, additional requests to establish datagrams are denied. One or more of
the permanent datagrams will need to be cancelled before others can be established.
Since the permanent datagrams are not automatically deleted when the SNP session is
terminated, this limit prevents an inordinate amount of these datagrams from being
established.
Permanent datagrams do not survive a power-cycle.
6.4.2 Communication Requests (COMMREQs) for SNP
The PACSystems serial ports COM1 and COM2 currently do not provide SNP Master
service, nor do they support COMMREQ functions for SNP commands. However, those
COMMREQ functions can be used with PCM/CMM modules that are configured to provide
SNP service. For more information, refer to the Series 90 PLC Serial Communications User’s
Manual, GFK-0582.
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