TCP communication between PC <-> PLC

[i don't know]

Hi all, I don't have experience PLC programming so it might be a stupid question.

I made a socket request to PLC and there is no problem to read and write but whenever completing the connection, PLC always sends RST packet see the attachment.

I want to know if this behavior is normal or there is something wrong to complete the connection.

Thank you in advance.

 

[Ken Roach]

Welcome to the PLCTalk forum community !

What make and model of PLC controller are you using ?

Are you configuring and testing a commercial protocol driver, or writing your own ?

 

[i don't know]

Welcome to the PLCTalk forum community !

What make and model of PLC controller are you using ?

Are you configuring and testing a commercial protocol driver, or writing your own ?

Thank you for your reply!

I'm not sure if this maker is known globally. Anyways it's LS electric and the model name is probably XGT series.

The below image is the protocol we are using i guess it's Modbus.

 

[Mark-]

Hello,

What "keepAlive" value do you specify when you open the socket on the PC?

 

[i don't know]

Hello,

What "keepAlive" value do you specify when you open the socket on the PC?

Hi Mark.
I didn’t use keepalive option when i open the connection.

 

[Mark-]

Hi Mark.
I didn’t use keepalive option when i open the connection.

Without more data, I would test against another program/device and if I get the same result I would really check what I am doing (port opening variables/message format/timing/etc.).

It looks like it RST 4+ seconds after the last transfer. Perhaps that is configurable in the device.

We have a free MODBUS TCP slave simulator on the website.