12
Operation
Reading and Writing Values Cyclically
If values are both read and written cyclically, it is also possible to
specify a mixture of these two methods in the "User_Prm_Data"
of the master. -
Positive and negative indices can then be defined in the required
order. -
What is important for cyclic reading, i.e. for the data transfer from
the slave to the master, is only the order of the positive indices. -
What is important for cyclic writing, i.e. for the data transfer from
the master to the slave, is only the order of the negative indices.
Examples
The variables already known from the previous examples art to be
read and written, i.e. the variables .AE11 to .AE14 are to be read,
and the variables .L1_YCOMPUTER and .L2_YCOMPUTER are
to be written. --
Variable Data type Direction PROFIBUS-DP index (decimal)
.AE11 REAL Read from slave 5
.AE12 REAL Read from slave 7
.AE13 REAL Read from slave 9
.AE14 REAL Read from slave 11
.L1_YCOMPUTER REAL Write to slave 255
.L2_YCOMPUTER REAL Write to slave 405
Possible "User_Prm_Data":
- User_Prm_Data = .., .., .., .., 5, 7, 9, 11, -255, -405 End_User_Prm_Data
- User_Prm_Data = .., .., .., .., -255, -405, 5, 7, 9, 11 End_User_Prm_Data
- User_Prm_Data = .., .., .., .., 5, 7, -255, -405, 9, 11 End_User_Prm_Data
- User_Prm_Data = .., .., .., .., 5, -255, 7, 9, 11, -405 End_User_Prm_Data etc.
There are 15 possible combinations for reading/writing these
values in the specified order. -
The 4 bytes at the beginning of the slave-specific parameter data
(.., .., .., ..,) are predefined and must not be used for defining
variables. - For details refer to section "Peculiarities of
"User_Prm_Data"". -
It is, however, recommended to use only one of the first two
variants which do not contain a mixture of negative and positive
indices and, thus, are clearer. --
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