SMC Sierra Monitor FS-8704-14, Руководство пользователя

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EtherNet/IP Driver Manual
Page 25 of 42
Appendix A.6.2 The PLC Program
The PLC program example below shows the minimum steps necessary to program communications with
the FieldServer. Depending on the real intended application, additional steps may be necessary for
completeness.
When the FieldServer is polling the PLC, all that is needed is to configure the tags being accessed.
Note that providing dedicated (long), flat structured (not UDT) tags for communications interface to the
FieldServer is preferable to polling single length tags in the PLC as it allows for much more efficient
communications and reduces complexity when mapping data in the FieldServer. It is better to think of these
tags as a “I/O Buffer” Interface that the real tags in the PLC get mapped to.
Appendix A.7 Read/Write Structures and Value of EIP_Structure_Handle
Some devices require that a specific value be used for the EIP_Structure _Handle field while writing the
structure to them. This value may be specified in the vendor documentation. If any non-zero integer is used
in a Read Map Descriptor for EIP_Structure_Handle, the value will be updated internally. The Map
Descriptor can then be browsed to obtain this value. Other devices do not validate this field when the
structure is written by the third-party device. A summary of the procedures to obtain this value is presented
below.
FieldServer as a Client:
•
Read
o
Use a value of 1, the driver will automatically update the field when a response is received from
the device. The Map Descriptor can then be browsed to obtain the value if required.
•
Write
o
Use the value supplied by the vendor OR
o
Use the value obtained in the Read Map Descriptor above OR
o
Use any non-zero value if the o
ther device doesn’t validate it
FieldServer as a Server:
•
Read
o
Use the value supplied by the vendor OR
o
Use the value obtained in the Read Map Descriptor above OR
o
Use any value if the o
ther device doesn’t validate it
•
Write
o
Not required
– use any non-zero value if the parameter is specified
Avoid Using UDT Types. The Data
will be read but the exact placement
of the data in the Tags and Arrays will
be hard to determine.
Tag Length must be equal to or greater than the
number of points being written/read.