How do I use the FB640, FB641, FB642 of the modbus rtu library

Hello, I do not want to use a cpu 341 because
 it is too expensive. I have a home automation
 with a cpu 315 2dp and I want now to couple 
it with an arduino to be able to add 
as many sensors as I want and be able
 to communicate with the internet.
 The communication must be done by the
 series dp with a rs485 lays. 
I know some have succeeded but 
I miss some elements. 
How do I use the FB640, FB641, FB642 
contained in the modbus rtu library
 of the step7 v5.5 library? 
Thank you for your reply

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Split from communicate between an arduino and a 315-2 dp .

Hello,

sry I see still so much missunderstandings. Why you want use CP341, look again to my post, you can also use CP340. I saw some this CPUs for 60 euro, only Arduino Mega is maybe about 20 eurs cheaper so don't understand to your info. Also again to that DP network, you need for Arduino DP interface, did you read about that systems? Again think if you have one or more Arduinos which need to be attached to bus. Via this info you need build your system also. Also another question if you talk about request to DP, you have RS-485 solution for your Arduino/s?

Update: in case you don't want to use some serial CP (I see this very cheap and quickly implemented), you can use 3-party SW libraries like Libnodave, Snap7 or other to create bridge SW on your PC between PLC and Arduino. Also you can then do what you want, read/write to SQL DB or other activities as you need.

Hello, The arduino can manage the modbus via 
an interface RS485. This interface can connect
 to the dp port of the cpu 315-2dp since it 
allows serial links. My problem is to understand 
how the fb640, fb641 , Fb642 function and in 
particular the declaration of the port that 
allows communication. So theoretically I do not
 need cp340 to communicate. 
On the other hand I want to try to understand
 the operation that you propose to me and 
I ask you if you can give me a concrete example
 of operation with an rs232 link, a cp340 
and an external microcontroller. 
thank you in advance for your help

Hello,

you can't use user defined serial communication via CPU's DP port, also mentioned Modbus. Only Siemens's supported protocols are available, mean what give Siemens for you as available, therefore I was recommended CP340. Look again, don't know if you've read my post about some bridge PC application use 3-rd party libraries, then you can probably also connect to that DP port and use some prepared functions via S7 communication system. With that CP340 and Arduino you can use your defined frames including exact defined Exchange data, prepared f.ex. inside S7-300 and send to Arduino or back again, as you need. As I said in my previous post, you can define cca 254 Bytes buffer for send and also for recieve, with max. speed 9600 you can have good results, you can make tests. Examples are here in Forum (standard examples are enough, you can implement ang change them as you need), also I was made some very same for my home flight simulator. My tests with big buffer and refresh with cca 1s is enough I think. Simply you must make tests, question is why you need this solution and for what reason.

Update: pls keep in mind that also due your requested number of Arduinos living on bus, correct CP340 interface is needed, mean RS-232 or RS-485. Again I ask if you have RS-485 solution for Arduino, because it has RS-232 ports. In this case you can connect only one Arduino to one CP340 RS-232.

Hello,

without to know which error you have, we can't help you. You can zip screenshots and attch them here. What protocol you set in CP341? What you did in Arduino? What is your idea about Exchange data between both systems? Also important is what type of CP341 you've bought - RS232 or RS485. Did you read my previous posts about recommendations?

sbousse

Hello I bought a cp 341 rs232 (341-1ah01-0ae0) v 1.0
 that I upgraded to 1.0.1. I have a cpu 315-2dp 
(315-2af01-0ab0 estand 03) I use step 7 v 5.5 I configured 
the station For the moment I just want to do communication 
tests without using the arduino to see how it works. 
So I use the example provided by siemens (cp 34x ptp com) 
and in particular this one (CP 340 PtP Connection) . 
I changed the address of the cp341 in the fc21 in 256.
When I load the whole in the cpu the led sf lights 
and the cpu stops. I do not know what to try. 
Thank you for helping me. 
Cordially

 

 hi sbousse,

the address on the PTP-blocks needs to be written in hex. Address 256 should be written 16#100

hope this works,

regards,

Hello,

you can't use instructions/blocks for CP340, you need use RK instructions. Look to documentation of CP341, also examples are here in forum. Also I hope you understand that you need use ASCII communication protocol, so set this to your CP341 card.

Update: I see still lot of missunderstandings, can you tell us what reason you have using FC21??? Better say what's name of FC21, is Siemens block or user defined FC???