Helmholz 700-651-CAN01, Manual

Page: 17 / 29

4.3 Consistent data
All data elements are defined as consistent data. This prevents
inconsistencies within the SDO and PDO data. The addresses of
the data elements can be located in the cyclic process image or
outside the cyclic process image. If the data is outside the cyclic
process image, access must be performed with the peripheral
access commands, “L PEx” or “T PAx.”
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All CAN messages are
defined as consistent
data areas in the
PROFIBUS.
If 3, 5, or more than 5 bytes are to be transmitted consistently,
SFC 14 “DPRD_DAT – read consistent data” and SFC 15
“DPWR_DAT – write consistent data” must be used to update the
data on older CPUs.
The blocks are described in the Siemens Manual “System and
Standard Functions for S7-300/400,” Volume 1, Section 16.
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The maximum number
of objects depends on the
CAN protocol used (11
bit/29 bit).
4.4 Maximum parameter sizes and address ranges
You can define maximum 44 slots (elements) for 11 bits or 36
slots (elements) for 29 bits. Of these, 6 elements are already
permanently assigned. The maximum number of assignable input
or output addresses is 240 bytes each, but together no more than
312 bytes.
Please pay attention to
the maximum parameter
sizes!
The parameters of the elements must not take up more than 120
bytes. The basic parameters already fill 7 bytes and each further
“DI” or “DO” entry requires three further bytes.
4.5 Parameterizing transmit and receive messages
Now the transmit and receive messages (“DI x byte,” “DO x byte”)
can be defined on the remaining slots of the DP/CAN coupler.
Please note the different
ID ranges for 11 bits and
29 bits!
DP/CAN Coupler 17