Based on LabWindows/CVI using Modbus communication by means of RS-232

[佩林]

Hello !

Thank you for your help.

There may be my mistake. I will solve the problem as soon as possible.

Thank you  again for your support and help.

Best regards.

xiepei. 

[VeryDetermined]

Hello,

(Sorry for duplication of the message. I posted it as new message but I couold not remove the old one)

I am trying to use the Modbus Test CVI code from RobertoBozzolo through a loopback RS232/RS485. However, I am facing CRC error almost every time for any data (doesn't matter write or read).

Unexpectedly some times when I am playing with the numbers and by clicking "write to slave" I get an answer from the port which I belive happens accidently (since using the same number again I receive CRC error). 

I have attached the sample answer I got. I think even there is a problem with the answer since function code does not mach.

Could anybody help me on that?

[RobertoBozzolo]

(Answered here)

[Dhasan]

I am getting the CRC error whether its read or write and writes work sometines. Is there any way to solve it 

[Dhasan]

Did you solve this issue?

[Dhasan]

did you solve the issue?

[RobertoBozzolo]

How you detect CRC errors?

Have you tried dumping messages and checking the CRC?

And have you tried checking the calculated CRC on write messsage?

[Dhasan]

Thanks for your reply. it was giving error 532, CRC error.  

I figured it out.  It was something wrong with the slave unit I was working. 

[Dhasan]

I am facing another issue. I am able to read from the device, but i cannot write anything to the device. It gives error 99. I/O operation timed out.

Is there any way to solve this.

I can write to my device when i use another modbus app which i got form internet.

Is there anything specific to the  Modbus testing program which i should take care of, when writing?

[RobertoBozzolo]

Which instruction is giving you this error? Can you post the relevant part of your code?

Since you say you can "read", this means you can write a query to the device and get a response from it, so you are already sending messages to your device without errors; given this, it seems possible that the problem is in how your write message is built and sent.