artem
Advanced Member level 4
Modbus question
I am, going to design modbus based controller network supporting hot insert with rs485.
Going through modbus spec i did not find diagnostic procedures to overcome the situation with possible data loss at hot swap (if there is any). As there are several missed OSI layers - 100 percent reliable message delivery is not guarrantied under modbus network . I suppose that some procedures could exist on user logic level because application (Modbus application protocol specification v1.1a) also lacks of that functionality .
Is there semiofficial diagnostic procedures to overcome temporary failures on serial line transmission via diagnostic functions capabilities ?
Of course in case of failure same message can be sent twice , but what if the slave did execute the message and response was not received properly by master and when it is not preferred to send same message twice as this can affect PLC controlled environment if executed second time.
Or do i have to secure hot insert or sap to make it fault free instead of trying to solve the problem in software way ?
There is no problem with modbus over tcp ip as tcp provides such functionality, but rs485 serial line does not .
I am, going to design modbus based controller network supporting hot insert with rs485.
Going through modbus spec i did not find diagnostic procedures to overcome the situation with possible data loss at hot swap (if there is any). As there are several missed OSI layers - 100 percent reliable message delivery is not guarrantied under modbus network . I suppose that some procedures could exist on user logic level because application (Modbus application protocol specification v1.1a) also lacks of that functionality .
Is there semiofficial diagnostic procedures to overcome temporary failures on serial line transmission via diagnostic functions capabilities ?
Of course in case of failure same message can be sent twice , but what if the slave did execute the message and response was not received properly by master and when it is not preferred to send same message twice as this can affect PLC controlled environment if executed second time.
Or do i have to secure hot insert or sap to make it fault free instead of trying to solve the problem in software way ?
There is no problem with modbus over tcp ip as tcp provides such functionality, but rs485 serial line does not .
