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Asked: 2026-05-31T05:54:59+00:00

I try to send FINS commands through UDP from PC (C#.NET) to PLC Ethernet

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I try to send FINS commands through UDP from PC (C#.NET) to PLC Ethernet module (Omron), but is not getting any responds from the PLC and have no clue where I can start troubleshooting.

PLC has a very simple ladder logic as follow:
If DM100 has value of #0001, then trigger on output 101.00. (Here, “Trigger” is just a symbol name for memory area D100, and “Output” is a symbol for output 101.00)
enter image description here

Then I wrote a piece of C# that performs FINS command of “Memory Area Write” which has command code of 01 02, followed by beginning address, number of items to be written, and the data. The C# code should write a value of #0001 to PLC’s D100 area to trigger ON on 101.00.

[deleted code that doesn’t work]..

The output 101.00 did not get triggered, nor I receive any exception.
I have made sure the following:

  1. Port, node and address configured correctly as confirmed by “Work Online” in CX-Programmer. I have also ping each IP to make sure nodes are connected.
  2. The UdpClient code is valid since I wrote a very simple server / client code that successfully send and receive packets.
  3. Ladder logic has no problem. I transfered the ladder to PLC and test out by Work Online in Monitor mode and setting D100 a value manually.

I suspect there is mistake in the fins_cmnd array, but as seen in my code, I have commented as detail as possible on each value; I can’t possibly find myself missing anything. I suspect I may not be parsing the hexadecimal correctly, but again, I have no exception to guide me.

I have no idea where and how I can troubleshoot. Hope someone here with FINS programming or PLC experience can offer me some help.

[ANSWER]
Thanks Porge for the link – that got me found out the problem. After a couple trails finally get it to work. See below for the working code.

string SERV_IP_ADDR = "192.168.250.1";
const int FINS_UDP_PORT = 9600;

byte[] sendPacket = new byte[]
{
    // Full UDP packet: 80 00 02 00 00 00 00 05 00 19 01 02 82 00 64 00 00 01 00 01

    // Header
    0x80, //0.(ICF) Display frame information: 1000 0001
    0x00, //1.(RSV) Reserved by system: (hex)00
    0x02, //2.(GCT) Permissible number of gateways: (hex)02
    0x00, //3.(DNA) Destination network address: (hex)00, local network
    0x00, //4.(DA1) Destination node address: (hex)00, local PLC unit
    0x00, //5.(DA2) Destination unit address: (hex)00, PLC
    0x00, //6.(SNA) Source network address: (hex)00, local network
    0x05, //7.(SA1) Source node address: (hex)05, PC's IP is 192.168.250.5
    0x00, //8.(SA2) Source unit address: (hex)00, PC only has one ethernet
    0x19, //9.(SID) Service ID: just give a random number 19

    // Command
    0x01, //10.(MRC) Main request code: 01, memory area write
    0x02, //11.(SRC) Sub-request code: 02, memory area write

    // PLC Memory Area
    0x82, //12.Memory area code (1 byte): 82(DM)

    // Address information
    0x00, //13.Write start address (2 bytes): D100
    0x64, 
    0x00, //15.Bit address (1 byte): Default 0
    0x00, //16.No. of items (2 bytes): only one address which is D100
    0x01,

    // Write Data
    0x00, //18.Data to write (2 bytes): value is 1
    0x01,
};  

UdpClient client = new UdpClient(); //create a UdpClient instance

try
{
    client.Send(sendPacket, sendPacket.Length, SERV_IP_ADDR, FINS_UDP_PORT);
}
catch (SocketException se)
{
    Console.WriteLine(se.ErrorCode + ": " + se.Message);
}

client.Close();
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1 Answer

  1. Editorial Team

    None of those strings will be parsed as hexadecimal. NumberStyles.AllowHexSpecifier allows the hexadecimal prefix “0x” but doesn’t parse the number as hex unless it is present.

    So you’d want (char)Int16.Parse("0x64", NumberStyles.AllowHexSpecifier).

    However, numeric literals in C# can be hexadecimal, so instead of doing all that you can just write 0x64 instead.

    I’ve just looked at this page as a reference for the protocol, and it would also be better to create the message directly as bytes rather than specifying Unicode code points and decoding those to bytes as ASCII. You can also use the array specification syntax to remove a lot of clutter:

    var message = new byte[]
{
    // header
    0x80, //(ICF) Display frame information: 1000 0001
    0x00, //(RSV) Reserved by system: (hex)00
    0x02, //(GCT) Permissible number of gateways: (hex)02
    0x00, //(DNA) Destination network address: (hex)00, local network
    0x00, //(DA1) Destination node address: (hex)00, local PLC unit
    0x00, //(DA2) Destination unit address: (hex)00, PLC
    0x00, //(SNA) Source network address: (hex)00, local network
    0x05, //(SA1) Source node address: (hex)05, PC's IP is 192.168.250.5
    0x00, //(SA2) Source unit address: (hex)00, PC only has one ethernet
    0x19, //(SID) Service ID: just give a random number 19

    // command
    0x01, //(MRC) Main request code: 01, memory area write
    0x02, //(SRC) Sub-request code: 02, memory area write

    // data
    0x82, //Memory area code, 2 bytes: 82(DM)
    0x00, //Write start address DM100
    0x64,
    0x00,
    0x00, //Word write: only one address
    0x01,
    0x00, //Write value of 1 to address DM100 (0000 0000 0000 0001)
    0x01, // - this value is 0xaabbccdd -> cc dd aa bb
    0x00, 
    0x00, 
};

    It also looks like there are some problems with your data section – according to the linked document the memory address should be 4 bytes, the write length 2 bytes, and the values 4 bytes each. These don’t match with what you have, so I’ve expanded that section.

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