Modbus driver

[atrejman]

Hi,
I have following problem with Modbus driver.
When I inhibit send command (write single coil) on firewall the command are not transmit from WinCC server to PLC. It’s work perfectly. But when I restore (on the firewall) sending command, WinCC server sends command form the past. May I prevent this?
Andrzej

[Gertjan van Schijndel]

To prevent a driver from sending commands you could set the following datapoint elements to TRUE:
_DriverX.MS
_DriverX.DC

[leoknipp]

Does your description mean that the driver is sending commands when the connection to the PLC is established again?
What is meant with "when I restore sending command" in detail?

Best Regards
Leopold Knipp
Senior Support Specialist

[atrejman]

For conduct some test I blocked function 5(Write Single Coil) on hardware firewall placed between WinCC Server and PLC. During this test I was trying send some commands to PLC but of course this commands were blocked by firewall.
Afterwards when I unblock function 5 on firewall, WinCC server immediately send commands which I was trying start during the test.

Andzrej Trejman

[Gertjan van Schijndel]

Does your firewall reject these commands? Or drop them?
In case the command is dropped the command can still be delivered when the firewall block is lifted before the timeout has occurred.