WIZnet Developer Forum

WIZ108sr UDP MODE: Transmit works but not recieving

Firmaware version 2.20

Hardware: Header pin 10 485_SEL is floating.
Netwotk: Static IP on both devices.
Serial: 19200,8,NONE,1,NONE No packing setup and serial command mode switch disabled
All Options default.

No problem configuring the WIZ108sr device.

I have the WIZ108SR configured for RS485 and UDP. I am using this setup for MODBUS protocol based devices. I can send register requests, via UDP, to my slave device and I am recieving a response from the device on the RS485 side. But the response never gets back through to the ethernet side. I am using a scope to see that the requests are in fact getting to the RS485 device and that it is responding. I have also looked at U2 pin 2 and it is toggling when I am sending data from the Ethernet side.

Any help appreciated

WIZ108SR can support on both 422 or 485.
You should be select one.
If you use 485, 485_SEL pin (J2:10) should be float (not connected).

Check 485_SEL pin.
If 485_SEL is already floated, check 485_SEL to be toggled(High -> Low).

when 485 output, 485_SEL is high.
when 485 input, 485_SEL is low.


Pin 10 is floating. And I can see that it goes high during transmit and low during receive. The high is 2.25V above base line and low is 500mV below base line.

Data signal on pins 3 and 5 looks good on both transmit and receive.

Just some additional information…

I switched to using TCP instead of UDP. I am getting basically the same thing. I set the 108sr up as a server and connect to it from my application. I then send a modbus register query from my application. In wireshark I can see the the connection being made, the data being sent and an ACK back from the 108. But no register data. On the scope, connected to the RS485 side, I can see the query data I sent from my application and the response register data comming back from the modbus slave. The data comming from the RS485 side is ismply not getting converted to either TCP or UDP data.

It seems to be likely to operate normal. But I don’t understand why 485 input doesn’t get thru ethernet.
Did you check the udp port numbers between WIZ108SR and test program, And Did you test another WIZ108SR?

If you have done already, you’d better return the module for RMA request to distributor or saler.


I did check the port numbers. I do believe I have a DOA WN108sr. I have a couple more coming.

Thanks for your help.


I have heard one error case a long ago.
In that case, when using 485-to-232 converter, The same as your case happens.

The reason is not yet known. I seems to likely to have some problem on converting 232 into 485.

Have you ever used something like that?


Thanks for your response…

I am not using RS232 at all. This is traight UDP/TCP to 485 and 485 to UDP/TCP.

I just received another device and have it connected now. I am seeing the same thing.

I send modbus requests via UDP. I can see the request datagram on Wireshark.

On the RS485 side, using a scope, I can see that the request has been converted to RS485, sent to the slave device and the slave device has responded.

I never see the response converted from RS485 to UDP datagram. Wireshark never sees the response datagram.

Any other sugestions would be greatly appreciated. If I can get this working then I am looking at purchasing several hundred of these devices per year.

Let me know what is your test pc IP & Port and what is WIZ108SR’s remote IP & Port?

I found some problem when test PC IP & port are different from WIZ108’s configured remoted IP & port.

I’ll tell you the result after more testing.

Thank you.

The IP and port of the test device is and 5000.

The IP and port of the WIZ108sr is and 5000. The remote IP and port configured on the WIZ108sr is and 5000.

What differential voltage level dose the WIZ108sr expect to see on the RS485 side? It puts out about a 6V differential but the test device is only delivering about a 4V differential back to the WIZ108sr. Could this be a problem? It’s good clean signal in both directions just different levels.

Also, I can ping the test device, the WIZ108sr and the host laptop ( that I’m using to run the configuration tool from a Windows command terminal. But I don’t seem to be able to ping anything sucesfully from the WIZ108sr confihuration tool. When I try I see something like the following in WireShark.

6931 431.045052000 NBNS 92 Name query NBSTAT *<00><00><00><00><00><00><00><00><00><00><00><00><00><00><00> (This line returns a header checksum error)
6961 432.558184000 ICMP 70 Destination unreachable (Port unreachable)

I can succsefully ping all of these addresses from the laptop where I’m running the WIZ108sr configuration too.

I’m so sorry to answer late.

I think the difference signal voltage is no problem.
BTW, I wonder why ping-test is failed using configuration tool.

According to the ICMP message described by wireshark, WIZ108SR doesn’t have the IP address or MAC address value?

[quote]6931 431.045052000 NBNS 92 Name query NBSTAT *<00><00><00><00><00><00><00><00><00><00><00><00><00><00><00> (This line returns a header checksum error)
6961 432.558184000 ICMP 70 Destination unreachable (Port unreachable)

Please check again the IP address and MAC address is validate.

Thank you.

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