Add set_pdu_length() about python-snap7 HOT 9 OPEN

For sure, but at the time the library was written it was an high value to negotiate with the CPU to receive a less or equal value. For my opinion, with the 1500, it need to increase the size of PDU, because of larger objects too. It is an endless question, but the library will not change his behavior.

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Why do you need to extend the PDU size ?
I can be interesting to use your ctor but it need some rework, I will look at it next week.
Moreover, it differ from the base snap7 ctor behavior not sure it will be accepted !

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Why do you need to extend the PDU size ? I can be interesting to use your ctor but it need some rework, I will look at it next week. Moreover, it differ from the base snap7 ctor behavior not sure it will be accepted !

I need a large PDU to do data acquisition of large db with hightest speed (DAQ rate).

I dont know what is ctor.

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Ok,
Normaly the PDU size is negotiated with the PLC, As for my knowledge a 1500PLC need to negotiate with HIS size (960).
What is your CP paramaters ? Do you change something on TIA Portal about the size of the PDU, if yes, please share some screenshots?

CTor : It's just shorthand for "constructor" - and it's what the constructor is called in Intermediate Language, too.

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Ok, Normaly the PDU size is negotiated with the PLC, As for my knowledge a 1500PLC need to negotiate with HIS size (960). What is your CP paramaters ? Do you change something on TIA Portal about the size of the PDU, if yes, please share some screenshots?

CTor : It's just shorthand for "constructor" - and it's what the constructor is called in Intermediate Language, too.

CP parameters ? I just did a regular snap-python db_read(). On plc side just normal security configuration to allow snap7 communication.

ok about Ctor.

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CP stands for Communication Processor, it is the "component" that handle the S7 protocol before processing (with the params like type of packet/Protocol, PDU, ...), historicaly it is to have the flexibility to handle other protocols with adding an CP Card (PROFIBUS-DP, OPC, OPCUA, PROFINET), like the CP-1542 to handle PROFIBUS DP on the 1500 Family.

If you don't use any CP card, you use the built in CP "component" from your 1500 PLC, this "component" negotiated with your external device. They commicate through S7 Protocol in your case, and will define the PDU size of their communication.

It is known issue in the low-lewel base library, see the answer of the maintainer of snap7

Your code is working but it is more like a "hot fix" until there is a change in the base snap7 package

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CP stands for Communication Processor, it is the "component" that handle the S7 protocol before processing (with the params like type of packet/Protocol, PDU, ...), historicaly it is to have the flexibility to handle other protocols with adding an CP Card (PROFIBUS-DP, OPC, OPCUA, PROFINET), like the CP-1542 to handle PROFIBUS DP on the 1500 Family.

If you don't use any CP card, you use the built in CP "component" from your 1500 PLC, this "component" negotiated with your external device. They commicate through S7 Protocol in your case, and will define the PDU size of their communication.

It is known issue in the low-lewel base library, see the answer of the maintainer of snap7

Your code is working but it is more like a "hot fix" until there is a change in the base snap7 package

??? I dont see any issue about negociating PDU size...

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The negotiated PDU Size is send by the PLC, if they ask for 480, the PLC will accept it because it has the capability to do it.

If you want more you need to declare it with a SetParam request, but, for me the 480 bytes values was for the old CPU 300/400, today the 1500 can do more, but the library didn't change this default value when negotiating with 1500 CPU's

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The negotiated PDU Size is send by the PLC, if they ask for 480, the PLC will accept it because it has the capability to do it.

If you want more you need to declare it with a SetParam request, but, for me the 480 bytes values was for the old CPU 300/400, today the 1500 can do more, but the library didn't change this default value when negotiating with 1500 CPU's

Ok I understand but no where says that the default PDU size sould be the maximum.

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