byte second.
For Example 2.1
One 16-bit register has the content 0x12AB, the register is transmitted:
High order byte = 0x12
Low order byte = 0xAB
9.2.3.4 Error Check Field (Checksum)
This field allows the receiving device to determine if a packet has been corrupted with
transmission errors. In Modbus RTU mode, the 16-bit Cyclic Redundancy Check
(CRC-16) is used. The sending device calculates a 16-bit value, based on the
information stored in the address, function and data fields using the CRC-16
algorithm and appends it to the end of the packet. The receiving device performs the
same calculation upon the reception of a packet. If the result does not match the
checksum stored in the packet, transmission errors have occurred and the packet will
be ignored by the receiving device.
9.2.4 Exception Responses
If a Modbus master device sends a noneffective command to a SPM93 or attempts to
read a noneffective holding register, an exception response will be generated. The
exception response consists of the slave address, function code, error code, and
error check field. The high order bit of the function code is set to 1 to indicate that the
packet is an exception response. Below Figure describes the exception codes
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