S7MultiVar reference - data limits

[Mateusz]

hello everyone,
I'm trying to read data using S7 MultiVar reference, everything works but when I try to read bigger space i've got error.

S7MultiVar Reader = new S7MultiVar(Client); // This method work

byte[] DB_A = new byte[1024];
byte[] DB_B = new byte[1024];
byte[] DB_C = new byte[1024];

int DBNumber_A = 1; // DB1
int DBNumber_B = 1; // DB2
int DBNumber_C = 1; // DB3
Reader.Add(S7Consts.S7AreaDB, S7Consts.S7WLByte, DBNumber_A, 0, 16, ref DB_A);
Reader.Add(S7Consts.S7AreaDB, S7Consts.S7WLByte, DBNumber_B, 0, 16, ref DB_B);
Reader.Add(S7Consts.S7AreaDB, S7Consts.S7WLByte, DBNumber_C, 0, 16, ref DB_C);
int Result = Reader.Read();

S7MultiVar Reader = new S7MultiVar(Client); // This method dosn't work

byte[] DB_A = new byte[1024];
byte[] DB_B = new byte[1024];
byte[] DB_C = new byte[1024];

int DBNumber_A = 1; // DB1
int DBNumber_B = 1; // DB2
int DBNumber_C = 1; // DB3
Reader.Add(S7Consts.S7AreaDB, S7Consts.S7WLByte, DBNumber_A, 0, 100, ref DB_A);
Reader.Add(S7Consts.S7AreaDB, S7Consts.S7WLByte, DBNumber_B, 0, 100, ref DB_B);
Reader.Add(S7Consts.S7AreaDB, S7Consts.S7WLByte, DBNumber_C, 0, 100, ref DB_C);
int Result = Reader.Read();

Now my question is if there is a data limit for this method?

Thanks for your kindly help

[Davide Nardella]

yes, all these conditions must be met:
1 - You can transfer Max 20 Vars
2 - The maximum amount of data (including the overhead) must be less then the PDU
3 - Every Var has 12 byte of overhead, the Multiread function has 12 byte of overhead.

[Mateusz]

Thanks David for explanation.
Is there another way to read data from several DB in the same time?
I'd like to read 400B from 8 different DB in the same time to not waste the time.

[Davide Nardella]

the only one is opening multiple connections to the same plc. using different clients of course.

[Mateusz]

thank one more time. One more question, how to configure PLC S7 300 to get 10 connections. Because now I can connect only 5 clients in the same time.
How to manage Connection Resources in PLC to get maximum quantity connections?
https://zapodaj.net/601a0b1a632f2.jpg.html

[Davide Nardella]

https://zapodaj.net/601a0b1a632f2.jpg.html
that's correct.
Hardware Configuration-->CPU property-->Communication
modify the values and then download the hardware config into the PLC.

As I can see you are using a 317 or 318 CPU, you should not have problems.

[Mateusz]

I have 32 connection resources but i can make only 5 Snap7 connections.
One Snap7 Conditions needs more than one PLC connection resources?
I'm using CP 343-1 Lean. I think this is a bottleneck.

[Davide Nardella]

Correct it's CP343-1 Lean the problem

[Mateusz]

I checked it on CP 343-1 (not Leen) and it is works.
I have another question, how to check if I added some variables to S7MultiVa? . Because if I not added any i will have a error during the writing to the PLC. Class S7MultiVar has private count, so I can't use it.
How to solve this issue?

[Davide Nardella]

can you explain better please ?
You should know if you added or not a variable.
You can modify the wrapper (it's in source form) to use a counter into the class.

[Davide Nardella]

can you explain better please ?
You should know if you added or not a variable.
You can modify the wrapper (it's in source form) to use a counter into the class.

[Mateusz]

i'd like to write a method which will send data to PLC depends if there are some data to send in each loop cycle( sometimes will be some data to send sometimes no). I can of course add additional variable to memorize that I added a variable to send.
ones again, thank you.