Delay in communication between CPU 315-2 PN/DP and CP 343-1 Lean

Good morning,

I'm using a CPU 315F-2 PN/DP and a CP 343-1 Lean; the ethernet communication between these devices is well projected and working (I'm using FB63 TSEND, FB64 TRCV, FB65 TCON, FB66 TDISCON in the CPU 315F and FC5 AG_SEND, FC6 AG_RECV in the PLC by CP 343-1 Lean side).

However it happened that on CPU 315F side, I was not able to get data "real time": there was a delay of almost ONE minute before I get the data sent from CP 343-1 Lean!

I solved the problem by reducing the number of telegrams sent by the CP 343-1 Lean. Actually the communication is almost "real time".

What I suppose is that the CP 343-1 Lean sent telegrams too fast, so the CP 315F-2 PN/DP was not able to "elaborate" them, and I also suppose there is a really big buffer where the telegrams are stored before they are elaborated.

My questions are:

1 - are there somewhere informations (manuals, data sheets, ...) about this buffer, where telegrams are stored? (I was not able to find anything on Siemens support site...)
2 - is it possible to make a real time diagnosis of this buffer, to understand its state and its filling? How?

If it will be possible to accede to these informations, it will be possible for me to improve a communication protocol, with a real congestion control.

Thanks in advance.

Filippo

Dear J_Bell,

the situation you described is exactly as it is.

I also thouth about improving a handshaking with the PN CPU as "director" of the

communication.

Actually this will result in a heavy modifications of the communication as I improved it in my program (with PN CPU countinuosly sending telegrams and also CP 343-1 Lean countinuosly sending telegrams).

If I will be able to know how fast is the PN CPU in elaborating the telegrams (how fast the

buffer I suppose it should exist is emptying), I will be able to adjust the number of

telegrams sent by CP 343-1 Lean, based on the ability of the PN CPU to elaborates them.

Actually I completely don't know if it is possible and how I could get these informations in

the PN CPU...

...maybe I will have to improve a real handshaking...

Thank you very much,

best regards.

Phi

Dear J_Bell,
thank you very much for the sample; the procedure described "is more or less" the one I follow to improve the communication.
I used also the "Open communication wizard" to get the parameters for the connection.

The main differences are:

- I create just 1 connection, not 2 like in the sample. In this connection I send and receive data (with FB63-TSEND and FB64-TRCV by PN CPU side and AG_SEND and AG_RECV by CP 343-1 Lean side).
- I set a PASSIVE communication for both the devices.
- I never close the connection with FB66-TDISCON

Actually I follow your suggest and I tried to improve a handshaking: what I get is even a better performance in the communication speed (compared to the one I had before).

Shortly, the PN open the connection, then after a timeout send a telegram; the CP 343 receive this telegram and it sends one too. the PN will send another message only after it has received the telegram from CP 343. By this way I will never fulfill the receiving buffer of PN CPU or CP 343-1 Lean, beacuse every device send only if it has previously received, and it won't send any other telegram until it will have received again.

Obviously I improved also some triks to restart the communication in case of need.

In the end, I get a communication at the maximum possible speed (depending by each device elaboration speed - I do not send more telegrams than every device could elaborates), always restarting, even if one device is shut down or for some reason the physical connection between the two of them is cut and then restored.

Thank you very much for your suggestions,

take care.

Phi