communication between S7-1200 and Danfoss FC302 using RS485

Hi everyone,

I need to read speed/ampere/torque from danfoss drive Dc302 on S7-1200 using RS485 RTU.

I tried many times to establish communication between them but failed.

could some one please send a sample program TIA for RS485 maybe I lose something.

Thanks alot

Hello Adham;

If you mean RS-485 Modbus RTU communications between a S7-1200 master and a Danfoss FC102 drive as a slave, here are a few links that should get you up to speed for your project; do not hesitate to come back to us for more détails once you have studied the documents below:

1. From our friend smiffy, a very informative document (and discussion) on the nbbasics of Modbus communication. As a refresher for anyone who has a bit of experience with Modbus, it is quite interesting. Fos someone who is just starting to work with Modbus, this information is critical,

Modbus General Description

2. documentation on the Danfoss FC102 as a Modbus RTU slave:

- Danfoss general Modbus document (includes a description of hardware, wiring and supported Modbus functions) :

http://files.danfoss.com/technicalinfo/dila/17/FRCC.ES.008.A1.02.pdf

- Danfoss FC102 Modbus register mapping: Command and status word, holding registers (Excel file)

FC102 Modbus Holding Registers

2. S7-1200 as a Master on Modbus RTU:

- S7-1200 Modbus RTU sample program (link available in the following FAQ) :

Which hardware and software components do you need to establish communication between SIMATIC S7 stations and third-party devices using the MODBUS RTU protocol?

Hope this helps,

Daniel Chartier

Thanks a lot for above data, I read them already before and tried but still having issue in communication.

Please find attached snapshots to be more clear.

FYI, the strange part that RX/TX leds of CM241 are not flashing and i checked many times the cable and hardware stuff but everything is good, i don't understand what is the problem

Waiting for your reply

thanks in advance

Hello Adham;

Could you post a schematic of your connections between the S7-1200 CM module and the drive? With the pinout désignations if possible?

When the TX/RX LEDs refuse to light up, it generally reflects a wrong electrical configuration.

Hope this helps,

Daniel Chartier

Dear Daniel,

Please find attached schematic for hardware connection, I hope its clear.

Thanks a lot for supporting me

Hello Adham;

It looks from your diagram that the electricalconnections should be correct.

So now, we have to look at why the Modbus polls are not working.

- how did you configure the CM 1241 , and please show us your MB_Master and MB_Com_load blocks, so we can see how you have set them up.

- how id the Modbus RTU protocol setup on the FC102?

Maybe the points discussed in this thread can provide clarification:

https://support.industry.siemens.com/tf/ww/en/posts/cm1241-no-answer-from-ptp-connection-instruction/116015/?page=0&pageSize=10

Hope this helps,

Daniel Chartier

The settings done to FC302 danfoss drive are:

slave address = 1 / baud rate = 9600 / parity = even / stops bits =1 / FCprofile selected / RTU protocol selected

The settings of TIA hardware config and software are as attached in picture.

Also I always receive status error = 16#8281 which means negative ack when writing module,

The funny point that I am only reading holding registers (function code 3) not writing !!!

Could you kindly support me 

Hello,

can you post screenshot from original documentation (needed register address with data type)? Do you have correct output from MB_COMM_LOAD DONE->OK? Look also to parameter Port if you assign correct value of CP module from HW cfg. This value can point also to this problem.

Yes I checked CM port number (270) and also Comm load block status is 16#7001

Attached is the mapping address of danfoss drive

the voltage address is 16120 as shown in pic and start addressing of code function 3 is 400,000 so that why I put 416120 also I tried other numbers but i dont issue is software code