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45
Accessing Parameters
Section 4-5
4-5-2-2 DP-V1 read/write sequence
The following illustration demonstrates the DP-V1 read/write sequence.
1. The PROFIBUS master generates an MSAC2_Write request with param-
eter instructions. The write instructs the Option Board to either read or
change a number of parameters.
2. If the MSAC2_Write request is valid, the Option Board responds with a
positive write response but no data. If the MSAC2_Write request is invalid,
the Option Board responds with a DP error.
3. The Option Board starts processing and executing the parameter instruc-
tions:
• While the Option Board is processing read instructions, it fills the result
data with parameter values. If the Option Board encounters an error,
the corresponding value is replaced with a PROFIdrive error number
(Refer to section
E-5 Parameter Value Formats
).
• While the Option Board is processing change instructions, it generally
does not generate result data. However, if it encounters and error the
result data is filled with either zero-data (no error) or the corresponding
error value and element index (Refer to section
E-5 Parameter Value
Formats
).
4. The master polls the Option Board with an MSAC2_Read request.
5. While the Option Board is busy executing the instructions, it responds with
a negative read response (state conflict).
6. Once the Option Board is finished with the parameter instructions and the
result is available, it responds with a positive read response, and the in-
struction data.
Note Consult the documentation of your PROFIBUS master to obtain information
on how the above sequence may be automated.
4-5-2-3 Accessing Option Board Parameters
The following example demonstrates how to use the DP-V1 Class 2 (MSAC2)
parameter channel to read an Option Board parameter:
Note It is outside the scope of this manual to explain the DP and DP-V1 headers
and trailers. They are however shown in the illustrations to make the context
of the message data visible.
Step 1 Open a DP-V1 Class 2 (MSAC2) channel to the Option Board (Refer to the
documentation of your PROFIBUS master on how to open and close a DP-V1
channel)
Instruct the Option Board to read parameter 965 (Unit profile code):
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