- 25 -
(3) Data
This is necessary data for a slave to take action based on the function code. The data
configuration differs depending on the function code. It consists of a starting register address,
quantity of data, or write data, etc.
Data is variable length of up to 125 words (250 bytes).
Refer to 6.2 “Function Codes” for the function codes supported by this product.
The maximum data size differs depending on the function code.
(4) Error check code (for Modbus RTU only)
A Modbus RTU (RS-485) message contains an error check code (CRC value) calculated by the
CRC-16 method to detect a request/response message error.
The data size of a CRC value is 2 bytes, and they are sent by the byte in the sequence of
low-order byte followed by high-order byte.
CRC-16 calculation uses data items from unit ID through the one before the error check code
(the end of the Data).
The slave calculates a CRC value based on a received request message, then compares it with
the CRC value (error check code) contained in the message. If they do not match, no response
is returned and no action taken.
Refer to 6.1.2 “CRC-16 Calculation” for CRC-16.
NOTE
NOTE
