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AcuDC 210/220 Series
interference when being transitted from one device to another. The check field
guarantees the device does not respond to error messages in order to improve
system reliability and efficiency. CRC16 error check method is adopted in Modbus
Protocol.
3. Error Check Method
Every message includes an error checking field which is based on the Cyclical
Redundancy Check (CRC) method. The CRC field checks the contents of the
entire message. It is applied regardless of any parity check method used for the
individual characters of the message. The CRC field is two bytes long, containing
a 16-bit binary value. The CRC value is calculated by the transmitting device, and
is appended to the message. The receiving device recalculates the CRC value
during reception of the message, and compares the calculated value to the actual
value it received in the CRC field. If the two values are not equal, an error will be
reported. CRC calculation is first started by preloading the whole 16-bit register
to 1’s. The process begins by applying successive 8-bit bytes of the message to the
current contents of the register. Only the eight bits of data in each character are
