Configuration

The server can receive Modbus functions via TCP/IP.

Modbus areas

The Modbus specification defines these four modbus-areas:

Modbus-areas

Data type

Access

Example

digital inputs (Discrete Inputs)

 

1 Bit

Read only

Configuration 1:

digitale outputs (Coils)

1 Bit

Read / write

Configuration 2:

Input registers

16 Bit

Read only

Configuration 3:

Output registers

16 Bit

Read / write

Configuration 4:

After the installation the modbus areas are mapped to the PLC areas. Check the article about the default-mapping.

The TwinCAT Modbus TCP/IP server configurator is used for configuring this mapping.

ADS-Access

If you want to access the specific modbus areas, you have to add these global variables to your PLC project.

VAR_GLOBAL
    mb_Input_Coils        : ARRAY [0..255] OF BOOL;
    mb_Output_Coils       : ARRAY [0..255] OF BOOL;
    mb_Input_Registers    : ARRAY [0..255] OF WORD;
    mb_Output_Registers   : ARRAY [0..255] OF WORD;
END_VAR
Further Information