BECKHOFF BC7300 - Manual (Page 44)

Appendix
44 BC7300
Blink block (PRG-CRC)
Creating the BOOT Program
The next step is the creation of a boot project. To achieve this, select,
when you are logged in, Online/Create boot project. The PLC LED flashes
while the boot project is being created. Now set the MODBUS slave
address and switch the Bus Terminal Controller off and then on again.
Remove the programming cable, and connect the MODBUS cable.
MODBUS Communication
Function 4 is used in order to obtain the states of the counters in the two
16-bit output words in the MODBUS master.