ModRSSim is now configured. Let's input values to registers in order to be sure that the OPC server polls registers properly. ModRSSim supports scripts written in Visual Basic - for instance, for generation random values (see Script Automation for details) - but here we will do simple manual input of values to registers.
Change values of several registers manually, and poll registers from Modbus OPC Server. Assume we need to poll 3 registers:
1.The Holding Registers region - a register address 12 - a data type word
2.The Input Registers region - a register address 6 - a data type float
3.The Coils region - a register address 8 - a data type bool.
Find those registers and input values to them
1. Holding Registers.
In ModRSSim settings, select the region Holding Registers and the data type word 16.
Now we have to fund the register number 12 and input a value to it.
In ModRSSim, register addresses are displayed in the standard appearance. A standard Modbus address defines a number of read function used, a number of write function used, and an address of the variable. In the standard addressing, there are 4 memory areas:
•Discrete flags (COILS): addresses 00001...09999, the read function 0x01, the write function 0x0F
•Discrete inputs (DISCRETE_INPUTS): addresses 10001...19999, the read function 0x02
•Input registers (INPUT_REGISTERS): addresses 30001...39999, the read function 0x04
•Stored registers (HOLDING_REGISTERS): addresses 40001...49999, the read function 0x03, the write function 0x10.
To transform a standard Modbus address to an address appearance of the OPC server (as well as to an appearance used in documentation of the most Modbus devices), you need do the follows:
1.Using the first digit of a standard address, detect a region the register belongs to.
2.Remove the first digit from a standard address and subtract 1.
We must solve the inverse task, therefore we need to add 1 to an initial address, and supplement the address with the respective region number. In or case, the register 12 is the address 400013. Find and double click it in the table.
A dialog to input a value opens. For example, input 50 and click OK - the value is displayed in the table.
2. Input Registers
Select the region Analog Input and the data type float 32.
Find the register 6 (300007) and input to it some fractional value - for instance, 12.25.
A value is written to an adjacent register as well. It is correct, because a float-type variable is 4-byte one and therefore occupies 2 Modbus registers - in our case, registers 6 (300007) and 7 (300008).
3. Coils
Switch to the region Coils. A data type in that region is always bool. The table displays values 0 (false) or 1 (true).
Find the register 8 and input to it 1 - that is, True.
Register values are set in the simulator, and now the OPC server can be configured.