Modnet - Can not talk to device

[Anonymous user]

Hi,

I have a system with Citect SCADA 2016. I want to communicate with a device over internet. Modbus RTU over TCP/IP will be used. ID of the device is 1  and port 80 is opened for modbus protocol. I will read a float value. Start address is 0.

I tested with Modbus Poll software and it works fine. I get the value.

But when i try with Citect, the driver is offline. In kernel it says that, can not talk to device.

I changed the citect ini parameter. I tried several options. (Initvar = 30000, 0 , 1 - InitVarType = 3,4) But nothing changed.

I used wireshark to diagnose. With modbus poll software, correct message sent to the target but not with Citect.

When modbus poll software used, first poll returns with timeout error but 2nd request comes with the correct return. Thats why i change some ini parameters too.

ConnectTimeout = 15000

Debug = 1

Delay = 100

InitVar = *as i mentioned above

InitVarType = * as i mentioned above

MaxOutstanding = 3

MaxPending = 3

PollTime = 100

Timeout = 5000

Watchtime = 30

Thank you.

[BevanWeiss]

ModbusTCP does NOT use port 80, it uses TCP port 502.

So are you testing using your modbus scanner in the same manner as Citect would be using (i.e. is your test valid)?

If you are getting a timeout on the first message using your test software, then this isn't a good start.

You should confirm that you can get successful communication over port 502 first (using telnet or tcping) this should be highly repeatable with a low error rate.  Only then would I bother trying to get actual ModbusTCP working.

[Anonymous user]

Thank you for quick answer.

I know that the default port of the modbus protocol is 502. But this one is configured as 80. And i can read the value with another software with modbus protocol from port 80. So everything is working great but Citect. So i think that something is wrong about modnet configuration. How can i diagnose it? How can i see what is going wrong?

[Anonymous user · Accepted solution]

Hi all,

I used Modbus driver instead of Modnet and it is communicating now.

[Juan]

Hi,

Modbus and Modnet protocols are different.
Modnet = HEADER (6 bytes) + Modbus

If the communication is with a Modbus RTU device, the appropriate protocol is Modbus if the type of gateway is (TCP-> RS232 / RS485).

In the case of using an EGX type gateway (TCP-> RS232 / RS485 + Modbus TCP-> Modbus) the correct protocol would be Modnet.

You can configure any port in the driver port settings in Citect. -I1192.168.100.1 -Pxxx -T

Regards,

Juan

[Juan]

Hi,

Modbus and Modnet protocols are different.

Modnet = HEADER (6 bytes) + Modbus

If the communication is with a Modbus RTU device, the appropriate protocol is Modbus if the type of gateway is (TCP-> RS232 / RS485).

In the case of using an EGX type gateway (TCP-> RS232 / RS485 + Modbus TCP-> Modbus) the correct protocol would be Modnet.

You can configure any port in the driver port settings in Citect. -I1192.168.100.1 -Pxxx -T

Regards,

Juan