1. Fbb-x510 CANopen
2. Parameterisation and Commissioning
3. Mapping the Fieldbus Boxes

Mapping the Fieldbus Boxes

Whereas in other fieldbus systems, the entire process image is usually transmitted cyclically, CANopen divides the process data into process data objects (PDOs ) containing each a maximum of eight data bytes. PDO mapping refers to mapping of the application objects (real time data) from the object directory to the process data objects. The CANopen device profile provide a default mapping for every device type, and this is appropriate for most applications. Thus the default mapping for digital I/O simply represents the inputs and outputs in their physical sequence in the transmit and receive process data objects.

The first 4 analog inputs or outputs are located in the second PDO.

These PDOs are accordingly occupied by the Beckhoff fieldbus I/O modules - if, for instance, no digital outputs are present, RxPDO1 remains empty.

In this way the PDO assignment for the Fieldbus Boxes is determined by the particular signal variants: digital input/output data is in PDO1, analog in PDO2, special signals in PDO3.

The Coupler Box modules occupy the PDOs automatically: during the start-up phase, the Coupler Box reads which extension box modules are present, and assigns the data to the PDOs. A distinction is made here between digital, analog and special terminals, and the PDOs are each occupied with one type. In other words, different types of data (such as digital and analog inputs) are not packed into one PDO, but a new PDO is started for each new data type.

Automatic PDO Assignment in Beckhoff Bus Couplers

The current mapping can be read by means of corresponding entries in the object directory. These are known as the mapping tables. The first location in the mapping table (sub-index 0) contains the number of mapped objects that are listed after it. The tables are located in the object directory at index 0x1600ff for the RxPDOs and at 0x1A00ff for the TxPDOs.

Process data assignment in the Fieldbus Box modules

The object directory entries in which the process data for the relevant module is located (default setting) is listed. The assignment can change as result of modifications to parameters (e.g. the process data length of serial interfaces).

Details of the data contents may be found in the fieldbus-neutral documentation covering Signal types (Fieldbus Box I/O Modules). You can find this on the internet in the Download area at http://www.beckhoff.com.