Description Of Cbc With Can Layer 2 - Siemens 6RA7086-6KS22 Operating Instructions Manual

Start-Up
The CAN (Controller Area Network) fieldbus is being used increasingly for industrial applications in
spite of its limited network length (max. 40 m with a data transmission rate of 1 Mbaud).
Data are transferred by means of telegrams. Each data message, the so-called COBs
(Communication Objects), has its own individual identifier and contains a maximum of 8 bytes of
user data. The CBC board uses the Standard Message Format with 11-bit identifier.
Simultaneous use by other nodes of Extended Message Format with 29-bit identifiers is tolerated,
but messages with this format are not evaluated.
Nodes on the bus determine from the identifier which telegrams apply to them. The COBs to be
sent and received by each node must be defined before data transmission commences.
The identifiers also determine bus accessing priority. Low identifiers gain faster access to the bus,
i.e. they have higher priority then high identifiers.
Errored telegrams can be reliably detected by means of a number of interactive error detection
mechanisms. A transmission is automatically repeated when errors are detected.
The figure below shows a diagram of the CAN architecture model that is oriented toward the ISO-
OSI-7 layer reference model. The CBC supports the functionalities provided by layers 2 and 7 of
this model.
Functionality according to layer 2
The user data from the user software (as COBs on byte level) must be transferred directly to layer
2 (see also the examples of PZD and PKW data exchange given further down).
Functionality according to layer 7 (CANopen)
Process data are exchanged rapidly by means of so-called PDOs (Process Data Objects)
analogous to the transmission method used for layer 2.
Parameter data are exchanged by means of so-called SDOs (Service Data Objects).
Application
Communication
7.7.3.1

Description of CBC with CAN Layer 2

User data are exchanged between the CAN master and the CAN boards on the drives, i.e. the
slaves. User data are categorized as either process data (control and status information, setpoints
and actual values) or data which relate to parameters.
Process data (PZDs) are time-critical and therefore processed faster by the drive (every 3.3 ms at
system frequency of 50 Hz) than the non-time-critical PKW data (parameter identifier value), which
is processed by the drive every 20 ms.
All settings required to operate the communication board are made in drive parameters (see
Section 8, function diagrams Z110 and Z111).
Process data (PZD) are categorized as either data received by the drive (control words and
setpoints: PZD Receive) or data transmitted by the drive (status words and actual values: PZD
Send). A maximum of 16 PZDs can be transferred in either direction; these are divided into COBs
with 4 data words each by the communication board. In other words, 4 COBs are required to
transfer 4 PZD words, with each COB requiring its own separate identifier. Identifiers are assigned
in the CB parameters as shown in the following diagram:
7-30
Device profile
Communication
profile
Layer 7 Application layer
Layer 3-6
Layer 2 Data link layer
Physical layer,
electrical
Layer 1
Physical layer,
mechanical
CAN protocol
specification includes:
CIA
- Device profile
DS 301
– Communication
CIA CAL
– Application layer
DS 201 .. 205, 207
CANopen
CAL
ISO-DIS 11898
CIA DS 102-1 Device Net ODVA
SIEMENS AG
SIMOREG DC Master Operating Instructions
05.05
Device net
Device net
profile
6RX1700-0AD76