Also known as Bisync. A byte-oriented communications protocol that organizes data into blocks of up to 512 characters framed with control codes that apply to the entire data set. Bisync was developed by IBM in 1966. BSC operates in half-duplex (HDX) mode, with the sending station transmitting one block at a time and the receiving device returning an acknowledgement following the receipt of each block.A positive acknowledgement (ACK) indicates that the data were received without error and that the sending station can transmit the next block. A negative acknowledgement (NAK) indicates that the data block was errored in transmission and that the sending station should retransmit it. Error control is based on a block checking character (BCC) that is transmitted along with the data.The receiving device independently calculates the BCC and compares the calculated byte with the received byte.There are six basic Bisync block formats, all of which comprise synchronizing bits, data, and control characters sent in a continuous data stream, block-by-block. See the illustration of a generic Bisync block in Figure B-4. The fields in the BSC block are as follows.