Maximum data length in DP/DP comm.

Hello,

In a profibus DP-DP network which consist of three CPU315-2dp ,

1.What is the maximum length of data that can be transferred between the master and a slave?
2.What is the limit for complete bus?

Local Siemens help desk says i can't transfer more than 32 bytes for each node, but in Siemens forum, i've read a thread which says it is OK to transfer up to 244 bytes per node..

Regards,

Yes, there is a total maximum of 244 input and 244 output bytes per node.

In addition to that, there is a limit to how much can be consistent.
You can configure consistent blocks up to 64 words (128 bytes).
More recent S7 CPU also have a limitation that max 128 bytes can be consistent. In the past the limit was indeed 32 bytes that could be consistent.

The limit that can be configured for a complete bus is CPU dependent. Check the specs for the individual CPU.

Thanks for the reply,

Only one point left unclear for me,now.

What is the maximum address i can define in that network?
I guess it should be ok if i addressed profibus I/O's like;

MASTER I500 , SLAVE O600 etc.

Well, i have tried it. HW configuration was consistent.
However;when i tried to move that data to bit memory in a FC, i could not download the FC to the slave, because the compiler gives a fault saying that the addresses i used in user program are out of S7-CPU315-2dp's range....

When i configure rows like Master I 80, Slave O4 i can communicate without any problems....

I want to use higher addresses in order to avoid possible conflicts, if new modules are added in the future.

Thanks in advance,
Regards,

The addressable i/o depends on the CPU.
The problem was that you assigned i/o addresses outside the "proces image" of the CPU. If you do that, you have to load the adresses into the user program via Periherial addresses (i.e. PIW600 in stead of IW600).
Because PI/PQ adresses are loaded immediately when encountered in the PLC code, it slows down program execution. So it is better to load from PIW to MW for example, and then use the Merker addresses in the code. Same with MW to PQW.

limit is 256 in and out in at bit level (OB1 PI image)
ie I0.0 and Q0.0 to I255.7 and Q255.7
limit is 2047 in and out at word level only (peripheral image)
ie PIW256 and PQW256 to PIW2047 and PQW2047
once you are dealing with the peripheral image data must be moved in and out of other memory such as a data block.
either PIW or PQW data cannot be viewed in the memory table, to view it view souce/destination data that you set up to read or write from.
the source data in a DB can be viewed and addressed at the bit level.

Thank you all for attention.

Regards,

How can we use Master Slave practically i.e. Masters QB0 byte, where it is read by Slave PLC (IB0 ?), how it is useful in realtime applications?

I confused, Please guide