Thanks a lot for helping me.
I reset all settings:
1- Factory Resetting PFC200-750-8202/025-002
2- adding all Modbus Libraries and PFC200 Libraries to the project
3- inserting Modbus_com, Modbus_Master_COM_Port and Modbus_Slave_COM_Port into Devices tree
4- Changing serial interface to RS485
3- set the PLC settings as follows:
Always update variables: Enabled2(Always in bus cycle task)
Bus cycle task: Main task
4- Modbus slave channel setting:
Modbus slave supports Function code 3 (read holding registers).
Access type: FC3
Modbus slave status is 'not running' again.
1- How is it that when slave is connected or not, I got the same results? nothing will change.
2- The data type I am trying to read from slave is Real. The setting in CODESYS defines data of type word in Modbus slave I/O mapping. How can I change it to Real?
3- Is it helpful to Change Master or Slave response timeout and time between frames?