dsc + modbus-rtu plc

[ALHIMIK]

Hello.
I use USB - RS485 converter to connect to my plc. I can read holding register with measured value and with assignment value, but i cant write assignment value.
I use i/o server with this settings -  Modbus-RTU, 9600/8N2, shared variable are (S)400002 and (S)400003.
Thanks

[Kelly_B]

Hi ALHIMIK,

Are you seeing an error when you try to write a value to the variables?  How are you writing to them?

Can you check the variables in the LabVIEW project using the Multiple Variable Editor to confirm that the Network-Published Access Type is set to read/write?

[K C]

Hi,

I don't know what SW you are using and how you have to define the ModBus command and address.

The addresses you mentioned are DCS addresses. 400002 for DCS is for ModBus command 4 (read register) at address 1 !!

If you want to write a register I think you have to use command 6 (Force Single register)

Kees

[ALHIMIK]

No i have not any errors, i write by distributed system manager. All shared variables are read/write.

[ALHIMIK]

To test this idea i create arduino slave device with simple modbus library and it works with 40000X command.I will try with command 6 thanks.