Documentation

This block does not have any input ports.

Output

Array of length Quantity that includes the values read from the given Data Table for the data range specified by the Index and Quantity parameters. The data type depends on the selected data table.

• For Coils and Discrete Inputs, the output port is a vector of the BOOLEAN data type, where the length of the vector is defined by the Quantity parameter. Each BOOLEAN element of the vector represents one bit.

• For Holding Registers and Input Registers, the output port is a vector of the UINT16 data type, where the length of the vector is defined by the Quantity parameter. Each UINT16 element of the vector represents one word/register.

Use Byte Unpack blocks to convert to signed values or floating-point numbers. You can unpack a vector of type UINT16 and length 4 to one double value.

Server Interface ID

Apply the Server Interface ID of the corresponding Setup block. Must range between 0 and 65535.

Node ID

Apply one of the Node IDs, which were defined in the Setup block. You can assign multiple Read blocks to the same Modbus node. Must range between 1 and 247.

Data Table

Select the Modbus data table you want to read data from. The options are:

• Coils

• Discrete Inputs

• Holding Registers

• Input Registers

Data Index

The first index of the data range you want to read. Must range between 0 and 65535.

• For Coils and Discrete Inputs, the parameter defines the start bit

• For Holding Registers and Input Registers, the value defines the start word

Data Quantity

The length of the data range you want to read. Index + Quantity must not exceed 65536.

Swap Bytes

The bytes of a register must be swapped if the sender and the receiver interpret the byte order in different ways (endianness). The Speedgoat real-time target machine uses little-endian, while some clients use big-endian If the swap option is enabled, all register values from the application context will be swapped before they are sent to the network. All register values received from the network will be swapped before they are submitted to the application context. The swap option only affects input registers and holding registers (transmitted by function codes FC3, FC4, FC5, FC6, FC16). Discrete inputs and coils are not affected. Use Byte Reversal blocks instead of enabling the global byte swapping if only single registers need to be swapped.

Sample Time

Defines the base sample time at which this driver block gets its sample hit. This parameter can also be set to -1 for inherited sample time. The units are in seconds.