Hello,

this topic is the continuation of :

S7-1200-CM1241-RS485 Modbus RTU problem

The manufacturer send me a new cables to connect to the rectifier to control.

Now I can use Modbus RTU and I am still a bit stuck of ho to do it.

I am attaching the documents for control of Modbus RTU.

I see how to read the holding registers , but I cannot see how to write to them.

There are some commands:

Register read command: Read Holding Register 0x03
Write Register command: Write Single Register 0x06

But I only know how to read and write by modifying the Mode parameter in MB_MASTER.

What could these commands be?

I need to send voltage and time for control and I need to read the voltage, current, time and errors.

Can somebody help me with this connection?

Thank you

Duris_I

Hello,

why not read Help to your MASTER block? You have there clear info (table) that MODE parameter sets this procedure - read or write. System is same as read, prior write any data you need to change expected buffer/memory elements with expected data to write and trigger MASTER block with MODE 1 or other value as help shows, nothing special.

 Hello,

thank you for the information.

I have connected the S7-1200 to the rectifier through the RTU.

But I cannot read the holding registers. The MB_MASTER_DB gives error 8383 every few seconds (could not capture it) and I cannot see where the error is. I have entered the array of WORD and trying to load the data in there, but it is not working. Im sure the connections are fine because the LEDs are indicating connection. As I read about the error it is something about wrong with the addresses, but based on the manual it should be fine.