Hello

I will use modbus-rtu to control a speed drive

As attached I will use CP341.

the question is will I need for HW dongle which installed in the CP back side??

Hello,

Yes. If yoú're skilled, you can prepare your own 'driver', in this case not.

Hello

do you use TIA Portal for programming?

then look at:

https://www.youtube.com/watch?v=G0nutiTYnUI

and here in classic world

https://www.youtube.com/watch?v=vArzfctgxJU

Bye Murof

Thanks for answer

Could you please explain more

Duris_I

Hello,

Yes. If yoú're skilled, you can prepare your own 'driver', in this case not.

 thanks for replay

Could you please explain more

I have CD came with the card

Hello,

simply if you're not skilled in programming your own communication procedures, you need buy respective dongle. In this case you have prepared comm blocks which you can use in your code to send/recv data. If you're skilled you can prepare your own communication sequences and not need buy dongle. Also here somewhere is some free 'library' or user communication solution without use of dongle. Look for Tibi68's topics.

Update: you can look in link with some example:

https://support.industry.siemens.com/cs/document/109474714/master-slave-communication-with-modbus-rtu-protocol-for-s7-300-and-et-200s-systems?dti=0&lc=en-WW

Update2: ok, look also to first topic in this conference, it's smiffy's Modbus topic about description of Modbus, can be also helpful for first before you jump to programming. Also I recommend this:

www.simplymodbus.ca