hello every one

i have a problem with determinig the registers number of Modbus

where in my project i am connecting CPu400 through CP443-1 to third part (DCS system) with MOdbus TCP protocol.. but the problem that i can't determine the modbus address list because i don't have any information in the configuration even in teh FB100 about the addresses.. and the designer of the DCS asks me in continue about the addresses....

so can any onw help me about that and tell me how can i determine the modbus register number?

an example of these number was indicated in the Open modbus TCP manual page 4-12 with the colour Grey but i did not understand from where are these numbers coming from?

thank you very much

Hello Eric

i would like to thank you very mush for your answer.. by this way i can understand that the Modbus register address has to be determind by the third parts..

with your answer i have understand what they have ment in the Manual OPEN MODBUS TCP section 5 " interpretation of the modbus register address is : the FB Modbus uses the register address transferred at its parameters START_x and START_ADDRESS. so it is possible to use register addresses from 0x0000 to 0xFFFF with each function code... "

i have written it again to associate it to your example..

and we can consider that depend on which addresses has specified by the third parts for Modbus, i can address my registers...

another example if we want to send to unknow third part and we write in the FB the following

DB_1:=W16#B // for example let us consider that we still transmitting the DB11

start_1:=W16#0001 // here by this way we still sending to the address 1 in the third part

End_1:=W16#007D

so in this example if we send some information to the precednet Telemecanique it will never receive the information in the wrong address and may be it will not receive anything... becuase there were specified MW4501 of hte memory for the modbus communication...

at the end if you want to communicate with any third parts by the Modbus TCP, you should have an idea which addresses has been specified for the modbus in third part...

please if i have written any thing wrong, i hope that you will correct me just by this way we can document a good example for this kind of problems...

thank you very much Eric

you have risolved a great problem for me..

because i have prepared my system to communicate with DCS but i don't know any idea about the DCS addresses ..and my client ask me in continue to determine the addresses of teh Modbus registers... and i have selected 1 to 125 because i don't konw any idea about his addresses .. and by this way, he who has to give me the addresses that he wants...

thank you again

hope you a nice day

Samer

Hi

excuse me .. can i ask you another qusetion

where i have noticed that you have written in your comment that in when i call FB100 i have to specify the same parameters but via DBxx.DBWyy ..

so in the example of the Open Modbus TCP when they have configured CP as a server then in the OB1 they have called FB100 they have never entered any parameter .. and i have donethe same for my system.. i have configured it as a server then i have called in OB1 the FB100 without entering any parameter in their inputs for DB_1, START_1 and END_1 ...etc. till this moment i did not test the communication but with your words i think that it will never work ....

i have attached an immagin about calling the FB100, FB200 and the FB200 configuration

they are equal to the example

NB: i have used DB11 to compress the data in an array of words, then i have FB200 in OB100 to assocciate the data which is coppied by their turns to DB224

my question is: are my configuration and my calls right?

thank you very much

samer

hello everyone

I have found just an error in what we have written above.. I would like to replied

S7 sends always their data starting from the address 40001 where this address correspond to the register 0 in the DBx, where the DBx is an array [0..124] of words in this case the register 0 correspond to 40001 and the register 124 correspond to 40125 adn any other registers will be addressed by an offset of the address 40001, for example if we have DB11 which is an array [300..425] of words by this way the data will be through the register 40301=300+ 40001 to 40426 = 425+ 40001

so let us consider that our program was written as following

DB_1=W#16#000B // DB11 that we have used to compress the data

START_1=W#16# 12C // start address is in 300

END_1=W#16#1A9 // end address in 425

by this way when the client ask to read the register 40301, S7 will pass the data in the register 300

i conclude that the addresses will always start respect to 40001 for the holding registers..

by this way what we have written for the example of 4501 could not be correct ....

if there is any thing wrong in what i have written or if the idea was not arrived correctly.. please i hope you make some replications..

thank you very much

all the best wishes.

hello Eric

thank you very much for your help... and the file that you have attatched ..

as i can see in it that you have recompiled the data block DB222 with all the communication parameters ..even that you have done that before within FB200 in OB200 "Cold start of the PLC"...

then you have attributed the communication parameters to FB100 within DB222 in the procedure FC82 all of that was to achieve the communication... and to determine the start and teh end addresses..

by this way i can see a little bit of difference respect the Manual, where in the example of the manual they have not attributed any value to FB100 about the DB_1 with its start and end addresses.... the same thing has been done for Server configuration...and i think depend on your example that i have to add "even that i am using a server configuration" the values to DB_1 and its start and end addresses while i am calling it through with OB1 ...

in this case i can conclude that all the parameters of the function FB100, which is marked as IN "input", must be attributed to a determined value in both of OB100 and OB1, and in both of Server and Client configuration...

by this file that i have attatched i should determine, while i am calling FB100 through OB1, the start and the end addresses of my S7 registers ...

is that right? please if there is any kind of error in what i have written, may i ask you to correct it ?

thank you again

all the best wishes

Samer