WIZ550S2E-485 Modbus TCP Server - connection reset by peer

Question

Hello, I’m trying to see if it’s possible to configure a WIZ550S2E-485 EV as a Modbus TCP to RTU gateway. WIZ550S2E configuration860×950 72.9 KB Now I’m trying to send a modbus request through the lib modbus, but then nothing is sent on the RS485 side, and I receive a Connection Reset By Peer error. This is the shortest C program that trigger the error (I’m omitting error checking for brevity). #include <modbus/modbus-tcp.h> int main(int argc, char** argv) { uint16_t buf[256]; modbus_t *ctx; ctx = modbus_new_tcp("192.168.11.100", 5000); modbus_set_debug(ctx, TRUE); modbus_set_slave(ctx, 2); modbus_connect(ctx); modbus_read_registers(ctx, 1, 1, buf); modbus_close(ctx); modbus_free(ctx); return 0; } Output: $ ./mdb_test Connecting to 192.168.11.100:5000 [00][01][00][00][00][06][02][03][00][01][00][01] Waiting for a confirmation… ERROR Connection reset by peer: read With Wireshark I noticed a Malformed Packet Error, but I don’t know if it’s the cause. (I can’t include a screenshot because new users are allowed to send only one image) I can’t figure out if there is something wrong on the configuration, on the C program or on the expectations. Thank you, Emanuele

mason · Answer

Hello Emanuele, Please refer to our Modbus library of WIZ550S2E code. You can see this through below link. GitHub Release v1.4.0 · Wiznet/WIZ550S2E-Modbus Added Modbus To use Modbus, you need a v1.20 Configuration Tool . v1.4.0 binary update Factory Reset with old Configuration Tool And then Use v1.20 Configuration Tool https://github.com/Wiznet/WIZ... I tested modbus function of WIZ550S2E through modbus poll and modbus slave It was no problem. image1462×790 55.1 KB Thank you.

scinz · Answer

Hi Mason, I tried to configure with Configuration Tool 1.20, but the result didn’t change. I was previously using v 1.31. With Modbus Poll the result is “Read Error”: Modbus Poll524×827 40.7 KB A capture with Wireshark gives this result: connection_reset.pcapng.zip (200,0 KB) connection_reset1518×764 176 KB that however I’m not able to understand. No idea of what could go wrong?

ostorezio · Answer

Hi Mason, I’m working on the same project as Emanuele. We don’t understand why the WIX550 is resetting the communication. As you see we tested the Master you suggested (Modbus Poll) and also another Master we’re using successfully with a different adapter (Moxa Modbus Gateway MGate MBxxxx). Probably there is a configuration that we overlooked. Is there any difference we should consider while moving from Moxa to WIX? Thank you for your attention, Ezio

ostorezio · Answer

Hi again, We did some progress, doing multiple testing, we found out there is a critical timing between the connection and the sending of the first Modbus request. If we send the request right after the connection, we get the “malformed packet” If we connect, and do nothing afterwards, the WIZ keeps the connection alive for 5", and then disconnects If we connect, wait 1" and send a Modbus request, Wiz disconnects right after the request The Modbus request is well formed, we sniffed it with Wireshark We keep track of connection/disconnection by looking at the green LED. Is this the expected behavior? I would say no, since Wiz is a Modbus slave (AKA Server) and therefore it’s connection must be kept alive forever and listening for incoming requests. Maybe we have to configure some timeout/keepalive parameter? Thank you again for your attention, Ezio

scinz · Answer

Problem solved! Connection password must be empty. Thank you for your help!