Modbus Process Image

Default config (without TwinCAT System Manager):

The data of the Modbus slave interface are stored in the allocated section of the BC8x50.

The input data from the master perspective are stored in the controller output section from address %QB1000 (Modbus address 30001, depending on master).

The output data from the master perspective are stored in the controller input section from address %IB1000 (Modbus address 42049 - depending on master).

The maximum data length is 512 bytes input and 512 bytes output.

Recommendation

We recommend limiting Modbus access to the flag area of the controller, master address 3 16385_dec or 4 16385_dec (3 4001_hex or 4 4001_hex, see Modbus interface). The flag area has a size of 4 kB and is not watchdog-triggered. The flag area is available for reading or writing.