HEIDENHAIN TNC 335 Technical Manual - Manual (Page 528)

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TNC 360 2 TNC data interfaces 8-21
The software handshake is very easy to achieve when transmitting with a BCC. The receiver sends
neither a positive (<ACK>) nor a negative acknowledgment (<NAK>), and the transmitter waits until
it receives one of these characters. When the buffer in the receiver is again capable of accepting
data, it again sends an <ACK> and the transmitter continues its data transmission.
It is also possible, however, to conduct the software handshake with control characters <DC1> and
<DC3>. If hardware handshake (EXT) has been selected, it is identical to standard data transfer and
to data transfer with a BCC (see Section "Freely configurable interfaces").