S7-1200 Modbus problem

Hi Experts,

I 'm trying to make Modbus (RTU) communication by using s7 1200.
I'm using CPU 1214C DC/DC/DC, CM 1241 (RS422/485)
I'm looking to read and write word registers in Load Cell Module connecting by Cm 1241 Rs422/485.
I'm trying for a long time to make communication between Cpu 1214 Dc/Dc/Dc as master and load cell module as slave but Done of MB_Master block respond to me as false and error also is false!!!

com. cable connection (Rs485)

Txd+ : pin3, Txd- : pin8

I attached my simple program.
Please I'm looking to help me to find where is the wrong in my simple program?!!
Thank you

https://www.dropbox.com/s/s35kuhw4c7qc41z/CM Test.zip
https://www.dropbox.com/s/q81uv5vocanlbp5/1.bmp

The MB_Master block is for Modbus RTU communication between 2 RTU units.

To get data from loadcell module you normally have to make a Point-to-Point (PtP) communication.

Look in the System Manual on page 565 (chapter 12.3) for how set up a PtP connection:
http://support.automation.siemens.com/WW/view/en/36932465

What manufacture / model is your loadcell module ?

Thanks JERA for your consideration
I'm using Delta load cell module(Dvp01lc-sl) and it's already is RTU unit

OK and thanks for the information on the loadcell.

If the loadcell is set up for modbus RTU communication, then you have to use the "MB_COMM_LOAD" instruction to configure a port for communication using the Modbus RTU protocol.

First when the "MB_COMM_LOAD" have established the connection, then you can use the "MB_MASTER" instruction.

Read this thread for setup of communication on S7-1200 and RTU protocol.
http://www.plctalk.net/qanda/showthread.php?t=83237&highlight=S7-1200+modbus

I solved the problem in my program
Any one need help or informations about Modbus RTU protocol
tell me and I will try to solve the problem

mahmoud shahien said:

I solved the problem in my program
Any one need help or informations about Modbus RTU protocol
tell me and I will try to solve the problem

Click to expand...

Hi mahmoud,
I am having problem in modbus comm in s7-1200. How can i see or change port ID. In hardware identifier, it says 270. But, it shows error as invalid port id. Please help me. Thanks in advance.

Cm 1241 rs485

mahmoud shahien said:

I solved the problem in my program
Any one need help or informations about Modbus RTU protocol
tell me and I will try to solve the problem

Click to expand...

Dear mahmoud shahien,
Please see attached, only Tx flashing nothing to receive we have CM 1241 module with V1.0
The message appear 8200 Port is busy processing a transmit request.
Thanks.

Hi to all.
I'm trying to connect with a s7-1200 12c/dc/dc/dc via cm1241 rs485 modbus rtu to a power meter but MS_MASTER_DONE response false!TX, RX not blinking.Please help me1
THANKS.

Hi everybody
I am trying to connect a delta temperature controller dtb4824 by a s7-1200 12c/dc/dc/dc and cm1241 rs485,modbus rtu,modbus master.when delta is not connect to cm1241 ,tx of cm1241 is blinking,but when I connect them tx,rx are turn on but not blinking. i want to read register of pv (address=1000H)and I put 44096 on data-addr of mb-master.I couldn'n read any thing.could any body help me?(excuse for my english I hope you could understand)