74• Fieldbus Controller 750-837, /02x-000, 750-838, /02x-000 Data Exchange
3.1.5 Data Exchange
With CANopen, the transmission of data is made using communication objects.
Each communication object consists of a CAN telegram with 8 byte data and a unique COB-ID (Communication Object Identifier) in the network.
The transmission of data, the triggering of events, the signalling of error states etc. is made using communication objects.
Parameters for the communication objects as well as parameters and data of the CANopen subscribers are filled in an object directory.
3.1.5.1Communication objects
•The fieldbus controllers 750-837, /020-000, /021-000 and 750-838, /020-000, /021-000 supports the following communication objects:
•32 Tx-PDOs,
for process data exchange of fieldbus node input data
•32 Rx-PDOs,
for process data exchange of fieldbus node output data
•Server SDOs,
for exchange of configuration data and for information on the state of the node
•16 Client SDOs,
for the request for the configuration data of the own node or of 16 other fieldbus nodes (master function)
•Synchronization Object (SYNC), for network synchronization
•Emergency Objekt (EMCY)
•Network Management Objects
-Module Control Protocols
-Error Control Protocols
-Bootup Protocol
WAGO-I/O-SYSTEM 750
CANopen
Fieldbus Controller 750-837, /02x-000, 750-838, /02x-000 |
• 75 |
Data Exchange |
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3.1.5.2 Communication interfaces
For a data exchange, the CANopen fieldbus controller is equipped with three interfaces:
•the interface to fieldbus (-master),
•the PLC functionality of the PFC (CPU) and
•the interface to the bus modules
Data exchange takes place between the fieldbus master and the bus modules, between the PLC functionality of the PFC (CPU) and the bus modules as well as between the fieldbus master and the PLC functionality of the PFC (CPU).
3.1.5.3 Memory areas
The controller uses a memory space of 256 words (word 0 ... 255) for the physical input and output data.
The controller is assigned an additional memory space for mapping the PFC variables defined according to IEC 61131-3. This extended memory space (word 256 ... 511 each) is used to map the PFC variables behind the physical process image.
The division of the memory spaces and the access of the PLC functionality (CPU) to the process data is identical with all WAGO fieldbus controllers. Access is via an application related IEC 61131-3 program and independent on the fieldbus system.
Access from the fieldbus side is fieldbus specific.
WAGO-I/O-SYSTEM 750
CANopen
76• Fieldbus Controller 750-837, /02x-000, 750-838, /02x-000 Data Exchange
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programmable fieldbus controller |
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memory area |
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for input data |
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fieldbus |
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modules |
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word 255 |
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word 256 |
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PFC |
IEC 61131 |
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program |
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input |
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variables |
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word 511 |
CPU |
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memory area |
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for output data |
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output |
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modules |
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Fig. 3-11: Memory areas and data exchange for a fieldbus controller |
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In its memory space word 0 ... 255, the controller process image contains the physical data of the bus modules.
1The data of the input modules can be read by the CPU and from the fieldbus side.
2In the same manner, writing to the output modules is possible from the CPU and from the fieldbus side. The value of the master is written to the output while writing on an output.
The PFC variables are filled in the memory space word 256 ... 511 of the process image.
3The PFC input variables are written in the input memory space from the fieldbus side and read by the CPU for further processing.
4The variables processed by the CPU via the IEC 61131-3 program are filled in the output memory space and can be read out by the master.
WAGO-I/O-SYSTEM 750
CANopen
Fieldbus Controller 750-837, /02x-000, 750-838, /02x-000 |
• 77 |
Data Exchange |
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In addition, the controller offers further memory spaces which, however, cannot be accessed from the fieldbus side:
RAM The RAM memory is used to create variables not required for communication with the interfaces but for internal processing, such as computation of results.
Retain The retain memory is a non-volatile memory, i.e. all values are retained following a voltage failure. The memory management is automatic. In this memory area, flags for the IEC 61131-3 program are filed together with variables without memory space addressing or variables which are explicitly defined with "var retain".
Note
The automatic memory management can cause a data overlap. For this reason, we recommend not to use a mix of flags and retain variables.
Code- The IEC 61131-3 program is filed in the code memory. The code Memory memory is a flash ROM. Once the supply voltage is applied, the program is transmitted from the flash to the RAM memory. After
an error-free start-up, the PFC cycle starts when the operating mode switch is turned to its upper position or by a start command from WAGO-I/O-PRO CAA.
WAGO-I/O-SYSTEM 750
CANopen