Com-Server Box-to-Box:

• Configure the RS485 2-wire mode in both Com-Servers using the internal DIP switches: 1, 2, 5 = ON, rest = OFF. The activation of termination (switches 6 and 7) depends on the existing RS485 bus structure. A physical RS485 segment may contain a maximum of two termination networks.

• Connect the power supply and the serial port of the Com servers to the RS485 bus, e.g. using the RS485 screw-in adapter.

  

• Assign the IP parameters (IP address, subnet mask, gateway) to both Com servers with WuTility.

  

• Set the serial transmission parameters on both COM-Servers to match the RS485 bus—this is usually identical on both COM-Servers. The handshake must be None.

  

• Activate the packeting option Interpacket Delay = 3 ms on both Com-Servers. This ensures that Modbus datagrams are transmitted closed in a network packet.

  

• Set up box-to-box mode on the Com-Server selected as the B2B master, including the option Activ. Packet Options.

  

• Check the option Activ. Packet Options also in the Com-Server operating as a B2B slave.

  

• Important: All settings made in the Com servers must be saved via the logout page.

  

In the best case scenario, the connection between the Modbus master and the Modbus slaves connected via the box-to-box connection is now working.

Both in B2B Master and in B2B Slave, the Connection State must show the status ’Locked’:

"Scanning," "Unlocked," and other messages indicate network-related problems. For example, the respective counterpart cannot be reached at all, or the TCP connection attempt is rejected. Check the following:

• The settings for the B2B configuration in the Master-Com-Server
• The basic IP parameters of the Com-Servers (IP address, subnet mask, gateway)
• The network connection between the two Com-Servers
• Whether firewalls in the infrastructure are blocking the connection

Errors reported by the serial transmission module (UART) during data reception are displayed here (framing or parity error).

All serial communication is initiated by the Modbus master, so that the Error State should first be checked on the connected Com-Server. First delete the current list to remove old errors. If new errors occur after manual updates to the website, the following causes may be possible:

• The baud rate, parity, or number of data bits are not configured identically on the Modbus master and Com-Server.
• The A/B and +/- connections of the RS485 bus are reversed.
• There are no (or more than two) terminations on the RS485 bus.

Regardless of the operating mode, all characters received (= Serial Rec) and sent (= Serial Trans) by the respective Com server are counted here. The website does not update automatically, so you must manually reload it (F5) to see the current values. Some examples:

1. Everything is fine:

2. The RTU slave does not send a response:

Possible causes:

• Inconsistent settings for serial transmission parameters on the COM-Server and RTU slave
• Reversed bus polarity on the RTU slave side
• Cable break, incorrect pin assignment, etc. on the RTU slave side
• Invalid Modbus addresses in the requests
• The packeting options on the B2B master are not configured or activated.

3. All counters are counting up correctly, but the RTU master still reports timeouts or errors for the RTU slaves connected behind the network tunnel.

Possible causes:

• The packeting options on the B2B slave are not configured or activated.
• Response timeout set too short on the RTU master