Modbus Slave, Siemens S7

Modbus on Siemens PLC? what is necessary?
Certainly not if keperluannya only for communication between Siemens PLC or HMI or other devices that support the standard protocol which is more reliable kinds of Siemens Profibus or profinet. The problem out there a lot of devices which provide the protocol but do not support Modbus protocols above. OpenModbus protocol selected that belongs more to the CP Toekang (CP-343/443), while for Modbus RTU menelorkan article Toekang need CP341/441, well that is ngak exist in the lab. And unfortunately this protocol can not be simulated by utilizing WinLC + Ethernet General, so that must have a dedicated Ethernet S7 PLC + CP.


To learn OpenModbus or Modbus / TCP PLC Siemens will Toekang divided into several stages. At this first stage, Toekang will make S7 PLC in this case S7-400 + CP443 as Modbus Slave (Server according to the terminology Siemens). As the Master (Client) will be used 3rd party tools such as Wonderware Modbus Poll or DASMBTCP as shown below: 

The steps to make the S7 PLC as Modbus / TCP Slave can be read here, which according to Toekang itself is not a simple step compared with Modbus setup in the PLC / DCS at the vendor laen.
Testing Results From the test results, Modbus / TCP are made from the Siemens S7 result was quite satisfactory as below: 

Even with the easy Toekang can read at once 360 ​​to the slave registers from Wonderware DASMBTCP that of their own configuration mambatasi only to 122 (for some reason just this hour, but from the Modbus / TCP Protocol Specification written 125) registers in one telegram. This is possible because FB100 as a library Modbus / TCP from Siemens that Toekang wear mechanism has been set to receive up to 625 registers (5 x 125) as below: 

From the observation data is processed in three stages (telegram). Each telegram will process 120 registers, and then will move to the next register 120.