Hi,

I have a question regarding profibus data communication limits. I have one S7 400 (new 6ES7414-3EM07-0AB0) and 5xPLC S7 300 (old 6ES7314-1AE03-0AB0).

Unfortunatelly S7 300 PLCs do not have ethernet interface, so I have to communicate via profibus between PLCs. I have some data to communicate, but these data are out of limits for AG_Recv and AG_Send functions. I have found that the limits are 236B (+4Bytes header = 240Bytes).

I started to decrese the data for communication due to limits. But before this I want to find out if there is any other way to solve this without decreasing the data amount.

Possibilities:

1) Decrese the transferred data amount

2) Use more connections (S7 400 can make 16 Profibus connections, so I could use 3*5 connections for my S7 300). Can I make two connections between the same S7 400 and S7 300 PLC ?

3) Use different transfer function except AG_Send, AG_Recv ? From my point of view and what I know from Profibus, 240B should be the limit of Profibus communicaiton capabilities.

Thank you for your support.

Best regards,

Georgio

Hi Georgio,

for S7-300/400 as DP Master you can use S7-Basiscommunication -with I_PUT/I_GET or S7-Communication with BSEND, BREV. With CP you can use AG_SEND_AG_RECV (FDL).

Please check the following manual (i.E. Page 117/118):

CPU-CPU Communication with SIMATIC Controllers

Regards,

Towome

Hi Towome,

thank you for the link, it is worthy !

I tried to manage the connection, but I was not succesful. S7 400 does not have CP and S7 300 is very old. S7 300 does not support S7 connection, and I cannot make FDL connection because I do not have CP :)

I thought that all Siemens devices can S7 connections 

Do you have any comments ?

Thank you.

Regards,

Georgio

Hello,

what exact order number of S7-300 CPU (better with firmware)?

Hi,

It is 6ES7 314-1AE03-0AB0 (The succesor is 6ES7 314-1AE04-0AB0).

Thank you,

Regards,

Georgio

The firmware I do not know, but the PLC application is from the year 1999.

From the product information I can see that year 1999 was the last year of production of this PLC..

Thank you,

Regards,

Jiri

Hello,

aaaaah apologize, now I see your first post order number. But this CPU hasn't DP port only MPI, you can't use DP communication, only in my opinion I_GET/I_PUT or other available as is described in that manual. If I can tell you, I have tested via CPU314 via MPI port some I_GET/I_PUT Exchange of data without problems (I think firmw. 1.1????), hope good remember. Yes, only little buffer of bytes can be used here, hope good remember about 70 Bytes, look to documentation. Maybe really your firmware doesn't support that instructions but make test for sure.

Hi,

I am sorry, I have CP profibus communication card connected to the S7 300 PLC, my apologize, I forgot to write it ! It is CP342-5, 6GK7 342-5DA00-0XE0.

But I cannot make the S7 connection even if I have this CP.. 

What can I do: only think is I can make FDL connection between S7 300 (CP342-5) and S7 400 (CP) - but I will have to buy CP card. I cannot make it with integrated profibus..

S7 connection is not possible even if I have this CP, this I do not undestrand :(

Thank you.

Regards,

Jiri

Hello,

in this case I see only one solution (also Towome already sugested) S7 communication, your S7-300 CP342-5 can act as Server, so from S7-400 use PUT/GET and in S7-300 only make some DB data available f.ex. Then you can change that data from S7-400 DP port (also if in CP) to S7-300 CP 342-5 via S7 communication without problems. In this case all make that CP, so age of CPU in this case doesn't matter in my opinion. Look to documentation how to prepare that in S7-400 side only (PUT/GET). Look to S7-300 side if you need also configure some instructions in case of S7 communication via CP342-5.

Update: carefully, your CP342-5 type can act only as Server in S7 communication!

Update: again pls check we what we know, if S7-400 has DP integrated or CP as DP, you can configure complete DP network as S7-400 MAster and all S7-300 as DP Slaves without problems. Then you can set I/O buffer and connections in S7-400 HW cfg and in each S7-300 only prepare DP instructions with DP buffer. Probably this solution I see best. Can you again confirm this?

Hi, thank you for your information.

You mean that I should configure DP network via NetPro ? I am not able to set S7 connection in NetPro. Get/Pu function require configured S7 connection. I quess.

Thank you.

Regards,

Jiri.

I am able to connect S7 300 to the same profibus network, but I cannot set the connection..