Siemens increase telegram size > 240 bytes

[Sefirod]

Hi guys,

I am working in a project where a SCADA (PcVue, from arcinformatique) needs to communicate with a Siemens S7-317 PLC.

Our comms are really slow, and after checking the data transfered using wireshark, I think is because the PLC splits the data in telegrams not longer than 240 bytes. Therefore, if I am requesting a frame of 5000 bytes, it has to split it in several frames of 240 bytes, which basically slows the communication.

I am using the protocol S7 IP Master, which uses a fetch/write in the PLC to acquire the data (i.e. the SCADA asks requests to the PLC of the data it wants). The S7-317 has a CP 343-1 coupler.

My question is:

You know any way to configure the PLC in order to send data to the SCADA using telegrams longer than 240 bytes?


Thanks for your help,


Eduard

 

[Jobbe]

Some models of CP cards have an option for this.
Look at the options for the CP card in the hardware config. Under the tab page "options" should be an option to allow messages larger than 240 bytes.

 

[Peter Nachtwey]

Hi guys,

I am working in a project where a SCADA (PcVue, from arcinformatique) needs to communicate with a Siemens S7-317 PLC.

Our comms are really slow, and after checking the data transfered using wireshark, I think is because the PLC splits the data in telegrams not longer than 240 bytes. Therefore, if I am requesting a frame of 5000 bytes, it has to split it in several frames of 240 bytes, which basically slows the communication.

Yes, the big problem is the time it takes to transfer packets over the back plane. It is best to get one of the S7-317 PN/DPs so that data goes directly to the CPU.

I am going to investigate how pig the packets can be for a S7 315-2 PN/DP. You do realize that 5000 bytes will not be sent in one packet.