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Communication / CBC
03.2010
6SE7087-6QX70 (Version AL) Siemens AG
8.4-16
Compendium Motion Control
SIMOVERT MASTERDRIVES
8.4.4
Data transfer via the CAN bus
8.4.4.1
General
With regard to the transfer of net (useful) data, a distinction is made
between parameter data (PKW data) and process data (PZD data) (see
also Section 8.4.1 "Product description").
CAN
identifier
CAN
identifier
CAN
identifier
CAN
identifier
CAN
identifier
Net data (8 Bytes)
Process data (PZD) words 1...4
Net data (8 Bytes)
Parameter (PKW)
Net data (8 Bytes)
Process data (PZD) words 5...8
Net data (8 Bytes)
Process data (PZD) words 9...12
Net data (8 Bytes)
Process data (PZD) words 13...16
PKW: Parameter ID word
PZD: Process data
Protocol frame
(Header)
Protocol frame
(Header)
Protocol frame
(Header)
Protocol frame
(Header)
Protocol frame
(Header)
Protocol frame
(Trailer)
Protocol frame
(Trailer)
Protocol frame
(Trailer)
Protocol frame
(Trailer)
Protocol frame
(Trailer)
Fig. 8.4-15
Structure of the net data in the telegrams of the CAN protocol
A CAN data telegram consists of the protocol header, the CAN identifier
(ID), up to 8 bytes of net data and the protocol trailer.
The CAN identifier is used for unambiguously identifying the data
telegram. In the standard message format, a total of 2048 different CAN
identifiers are possible and, in the extended message format, 2
29
CAN
identifiers. The extended message format is tolerated by the CBC but
not evaluated.
The CAN identifier also specifies the priority of the data telegrams. The
lower the number of the CAN identifier, the higher its priority. If two or
more bus nodes want to send data telegrams at the same time, the
CAN telegram with the lowest CAN identifier and thus the highest
priority is accepted.
A maximum of 8 bytes of net data can be transferred in a CAN data
telegram. The PKW area always consists of 4 words or 8 bytes, i.e. the
data can be transferred in a single data telegram.
In contrast to this, the process data area for MASTERDRIVES consists
of 16 words, i.e. a total of 4 data telegrams are needed to transfer all
possible process data.