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Appendix B. Driver Notes
Appendix B.1. Understanding buffer types and Map Descriptor functions
The following DP_Buffer types and Map Descriptor functions are normally used together when the FieldServer is used as a DP Master:
DP Master:
DP_Buffer | Function |
Output | WRBC |
Input | RDBC |
The Buffer functions are reversed when using the FieldServer as a DP Slave:
DP Slave:
DP_Buffer | Function |
Output | RDBC |
Input | WRBC |
The diagram below explains the data flows for both buffers when using the FieldServer as a DP Master:
Note that for the Input buffer, the data is coming from the external DP Slave and is transferred into the DP Master card’s internal input buffer. The Map Descriptor being of the RDBC function ( Read Data Block Continuous ) transfers the data from the card buffer into the FieldServer’s Data Array packing it correctly according to the specified DP_Type.
For the Output buffer, the data is written from the FieldServer’s Data Array by the WRBC function Map Descriptor ( Write Data Block Continuous ) into the DP Master card’s internal output buffer from where it is transferred across the Profibus network to the external DP Slave’s input buffer.
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