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I try to briefly explain my problem.
My goal is to communicate with the plc (S7200 CPU224) in order to read and modify variables during program execution.
I am in possession of an interface rs485, rs232 to Ethernet (USR-TCP232-24) of which I enclose a picture and the manual.
From what I understand the plc on db9 connector has two dedicated pins to rs485 (3 and 8), but it seems that the term refers only to the standard RS485 electric, while the communication protocol, I believe remains MPI.
To overcome this, I set the communication mode of the plc on port 0, as Modbus slave and tried to communicate with the plc to pc. Specifically referring to this tutorial:
http://program-plc.blogspot.it/2014/09/how-to-make-simple-modbus-rtu.html
By monitoring the virtual com, however, it seems that the plc always responds with a double 0 in binary.
Where am I wrong? Should I put the resistors 220 and 390 ohm output from db9 plc?
If I can not do it this way, what is the solution? And 'need for a power cable mpi rs232? Why can not I use the rs485?
USR-TCP232-24 Img:
https://support.industry.siemens.com/tf/ww/en/postattachments/preview/?attachmentId=55716
USR-TCP232-24 Manual:
https://mega.co.nz/#!8thyWBoA!BXr2M_ZlzQaFfKsMZGrswhVsQc5GFQSG4-sdADJ-eWg
Thanks for your help and sorry for my English is not too good.
My goal is to communicate with the plc (S7200 CPU224) in order to read and modify variables during program execution.
I am in possession of an interface rs485, rs232 to Ethernet (USR-TCP232-24) of which I enclose a picture and the manual.
From what I understand the plc on db9 connector has two dedicated pins to rs485 (3 and 8), but it seems that the term refers only to the standard RS485 electric, while the communication protocol, I believe remains MPI.
To overcome this, I set the communication mode of the plc on port 0, as Modbus slave and tried to communicate with the plc to pc. Specifically referring to this tutorial:
http://program-plc.blogspot.it/2014/09/how-to-make-simple-modbus-rtu.html
By monitoring the virtual com, however, it seems that the plc always responds with a double 0 in binary.
Where am I wrong? Should I put the resistors 220 and 390 ohm output from db9 plc?
If I can not do it this way, what is the solution? And 'need for a power cable mpi rs232? Why can not I use the rs485?
USR-TCP232-24 Img:
https://support.industry.siemens.com/tf/ww/en/postattachments/preview/?attachmentId=55716
USR-TCP232-24 Manual:
https://mega.co.nz/#!8thyWBoA!BXr2M_ZlzQaFfKsMZGrswhVsQc5GFQSG4-sdADJ-eWg
Thanks for your help and sorry for my English is not too good.