Example

The following figure gives an example of how a block check character is created for an acyclical message of type PDU 85_hex with 3 process data items. The XOR logic operation on the characters SD1 – PO3_low results in the value 13_hex as the block check character BCC. This BCC will be sent as the last character of the message. The recipient checks the character parity after having received the individual characters. Following this, the block check character is created from the received characters SD1 – PO3_low in accordance with the procedure below. The message has been correctly transmitted if the calculated and received BCCs are identical and there is no character parity error. Otherwise, a transmission error has occurred. The message may have to be repeated.