Balluff BIS M-370-000-A02, Manual, Page: 136 / 198

PROFIBUS INTERFACE
129
9
Bit 2 is set by the Slave after it completes resynchronization, and then cleared once the
Master has acknowledged that resynchronization is complete.
Bit 3
is set by the Slave when the total CBx response being returned to the Master is larger
than the space available in the Input Buffer (or that the packet being returned is a fragment,
and that there are more fragments to follow). This bit is cleared for the final fragment of a
fragmented response
– and so the Master can know when all the fragments of a response
have been returned from the Slave.
Bit 7
is set to 1 as soon as the Slave has been successfully initialized at power-up, and
remains at 1, to conform to Balluff’s proprietary Protocol.
Byte 1 : is always 0.
Byte 2 : contains the length of the packet in bytes (CBx response or response fragment) to be
sent back to the Master.
Byte 3 through Byte N-2 are used for the actual CBx response or response fragment to be
sent.
Byte N-1: The final byte of the Input Buffer is the Data Consistency Byte for the Input Buffer.
It is a copy of the Input Buffer Control Byte. The Master should check that these two bytes
are the same, before considering the Input Buffer’s data to be valid.
NOTE
The input and output buffers can exceed 64 bytes. The combined total of the
input and output buffers cannot exceed 152 bytes.
9.5.1 Example 1: Normal Command/Response Sequence
For this example, the Master will send a CBx “Read Tag ID” command to the Slave (the
Processor unit) to read an 8-byte tag
ID from an RFID Tag. First we will see a “Tag Not
Found” error (assuming that the tag is not read) and then we will see a successful read of the
Tag ID.
We will assume for this example that both the Input and Output Buffers have been configured
to 32 bytes each. This means that the processor unit response (for this command) can fit
entirely in the input buffer, and no fragmentation is required.
Sending the command:
In Byte 2 of the output buffer the Master places the length (in bytes) of the data packet (CBx
Command) we are sending. In this case the CBx command we are sending is 12 bytes. This
length is the length of the command bytes we are interested in sending, not the full size of
the buffer. The length also does not include the “Data Consistency Byte” at the end of the
buffer. That is just a mirror of the Control Byte.
In Byte 3 through Byte 14 the Master places the 12 bytes of this particular CBx command.
Some CBx commands are larger, but all will be at least 12 bytes, even if some of those 12
bytes are not actually used.