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12. Profibus Protocol Implementation
12.1. Protocol Specification
The protocol is based on the standard Profibus-DP V0 protocol, with the following basic specifications:
• Mode : RS485
• Baudrate : 9.6k, 19.2k, 45.45k, 93.75k, 187.5k, 500k, 1.5M, 3M, 6M, 12M
• Autobaud : Supported
• Freeze Mode : Not Supported
• Sync Mode : Not Supported
• Slave Node Address Change : Not Supported
• Diagnostics : Not Supported
• No PTO or PNO certification available (Not mandatory for Profibus DP)
12.2. Master-slave concept
The profile is based upon the master-slave principle. This means that all communication is initiated by the master and a
reply is generated by the slave.
All buffers should be full length consistent.
12.3. Buffer structure
The profile can be used for buffers with differs length: 8, 16, 32 and 64 bytes. This buffer is split into 2 parts:
• Header (B0) : 1 byte
• data section : n * data record (7bytes)
The buffer length is thus defined as follows:
Number of data records (n) Total buffer length Total used buffer length
1 8 8
2 16 15
4 32 29
8 64 57
NOTE: Not all functions allow more than 1 data record to be transferred. Basically read operations can be handled for several data records
in 1 cycle, while write operations are only valid for a single data record at a time.
12.2.1. Header
The header is a bit encoded 1 byte value. The interpretation is different for Master > Slave and Slave > Master
communication.
Master > Slave
The header is split into 3 areas:
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