Using Siemens CP341 card with 3964R protocol


Thread Starter


I have a CP341 Siemens card. I need to write a simple program to fetch / write data to a third party device. For instance, I need to fetch a value contained in DB3, Word 1 (of the third party device) to my S7 300 PLC DB10, Word 4.
Also I need to write a value contained in my S7 300 PLC DB20, Word 6 to DB3, Word 4 (of the third party device.

Are there anyone who can help me.

D. C. Pittendrigh

Hi All

I can probably help you, I have written a driver from scratch for wonderware for a CP340 card, so I have already been there.

Step no.1

Is the "3rd party device" another Siemens PLC which is 3rd party due to its not bring S7? If not you will not need to use P3964R.

If it is a Siemens device please let me know more about it.

If non-Siemens you must have a description of the protocol for making the device write your data value into DW??

Let me know more and I will tell you step 2

Donald Pittendrigh

YiewMing, Foong

Hi, Thanks for the response.

The "3rd party device" is a non-siemens product. It is actually a special controller for regulating fats content in the milk industry. It behaves as slave. That means the master will be the CP341 card that I have. This device supports several protocols and one of them is of course, 3964R.

The literature from this "3rd party device" says that it has various data (e.g. % fat content, flow rates etc...) located in DB3,DBW0 and so forth. The other information provided is basically how the 3964R protocol works. Since both devices is supporting this 3964R protocol, I presume this should be transparent to the user.

My difficulty is actually programming the Step 7 in the S7-300 using the Standard function block P_RCV_RK and P_SND_RK to fetch/write data from/to this "3rd party device".

I tried reading the Siemens literature of the CP341 card, but it doesn't really help.

Thanks again for your response

YiewMing, Foong

D. C. Pittendrigh


I have attached a backup copy of the S7 programs which can be used to implement this function as described. These samples are available on the
CP341 disks from Siemens and are generally self explanatory, if you cannot solve the problems from this information please contact me again.

Donald Pittendrigh