Function code descriptions

With this function code, one 16-bit value or multiple 16-bit values can be read. This function can be applied to NanoJ objects (see NanoJ objects) or process data objects (min. 4-byte alignment, see Process data objects (PDO)).

This function code can be used to write a single 16-bit value. The function can be used on process data objects (see Process data objects (PDO)).

With this function code, one 16-bit value or multiple 16-bit values can be written. The function can be applied to NanoJ objects (see Process data objects (PDO)) or process data objects (see NanoJ objects).

With this function code, one 16-bit value or multiple 16-bit values can be simultaneously read and written. The function can be applied to NanoJ objects (see Process data objects (PDO)) or process data objects (see NanoJ objects).

This function facilitates simple access of the CANopen object dictionary. Further details can be found in the following documentation:

Definition of the request and response:

Protocol options Range

Protocol control:

The "Protocol control" field contains the flags that are needed for controlling the message protocols. The bytes of the "Protocol control" field are defined as follows if the "extended" flag was set (the second byte is otherwise omitted):

The most significant bit (MSB) is bit 0 for "protocol control" byte 1 and bit 8 for "protocol control" byte 2. The least significant bit (LSB) is bit 7 for "protocol control" byte 1 and bit 15 for "protocol control" byte 2.

Address and data range

The address and data range is defined in the following table:

Example:

To read object 6042_h:00_h (16-bit value), the following message must be sent by the master (all values are in hexadecimal notation).

Shown as an additional example below, a sequence of Modbus messages is sent from the master to the slave to rotate the motor in "Velocity" mode:

Below are two examples for reading an object:

This function code is used to read out the complete object dictionary.

To start or restart the reading out of the object dictionary, subfunction code 55_h must be sent. This code resets reading out of the object dictionary on object 0000_h. All subsequent object dictionary frames must then contain subfunction code AA_h. At the end, once all objects have been read out, an "Error Response" is generated with the abort code "No data available".

The format of each "read object" is as follows:

Example

All of the following numerical values are in hexadecimal format.

Start reading of the object dictionary with request:

The response is:

Read out the next part of the object dictionary with the request:

The response is:

Repeat reading of the object dictionary with the previous request until the response is an error:

This function code is used to read out the complete array or record from the object dictionary.

To start or restart the reading out of the array, subfunction code 55_h must be sent. This code resets reading out on the object with subindex 00_h. All subsequent requests must then contain subfunction code AA_h. At the end, once all objects have been read out, an "Error Response" is generated.

The format of each "read object" is as follows:

Example

All of the following numerical values are in hexadecimal format; the index of the object that is to be read is 2400_h.

Start reading of the array with request:

The response is:

In case of an error, the following exception codes may be contained in the response depending on the function code:

For further details, refer to Modbus specification MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1b3.