Hello dolby;

First, there are a few free downloadable Modbus master simulator programs on the web. We used Modscan32 for our Modus tests:

Download ModScan32. - WinTECH Software

This guide could be useful:

Modscan32 Quick Start Guide for ModBus or Johnson Controls N2

https://support.industry.siemens.com/cs/ww/en/view/23907920

Now, as far as connections on the Com port (very probably RS-232C), you should find out what model of CP 341 you have in hand. There are RS-232 (6ES7 341-1AH02-0AE0) and RS-485 models (6ES7341-1CH01-0AE0).

If the CP 341 has a RS-232 interface 9same as your COM port), you only need to check the pinout for the module and build a cable that connects with the right COM port pins. If it is a RS-485 communication module you need a converter from RS-232 to RS-485 (there is a large number of manufacturers that can be found on the web), then use a proper cable between the converter and the CP 341. You will probably have to go to an electronics shop to purchase a 15-pin Sub-D connector to build the cable for this interface.

See Appendix B of this manual for the pinouts for different models of CP 341.

SIMATIC S7-300 CP 341 Point-to-Point Communication, Installation and Parameter Assignment

https://support.industry.siemens.com/cs/ww/en/view/1117397

Hope this helps,

Daniel Chartier

Thank you for quick reply.

I was wondering is there some way of using for or while loop in ladder or fbd? The reason I need loops is that I that I have a lot analog sensors and for every sensor I need to distinguish 5 different levels. So the idea is that I use for loop to read from and write to db, and use it for every sensor, so I don't need to do it manualy for every single sensor.

Any help good;)

Hi again, i have wired plc, and whole hardware configuration and everything works fine, but the cp module blinks on the start up, but after that doesn't seem to react. I connected pcmcia card which is giving me rs232, and then through rs232/rs485 converter to cp341. The problem is that I have radzio modbus, (because modscan32 needs key, so I have to use free master simulator)

When I set device id as slave address (222), and set up holding registers from 0 to 512 (length), I got the message "modbus messagge timeout". I've lost whole day and I didn't have any success. Does someone know what may be the problem?

How did you calcualate 1536?

I have configured DB22 in the hardware configuration of CP341 for functions fc 03/06/16 and in pc app for slave id I added slave address, but I keep getting modbus timeout.

RX and TX LEDs on CP341 are not blinking at all, like there is no communication..

Sorry I forgot to say, diagnostical buffer in online mode says that cp accepted given parameters, and that cpu went from stop to run.

From that side everything looks ok, I've made changes in device manager of the pc(baudrate, parity) but I keep getting "modbus message timeout"

Hello,

for first check if propper output goes from your PC application via that converter port. This is basic.