HEIDENHAIN MANUALplus 620 Technical Manual page 1786

Handshaking
1786
At the end of every block, the receiver checks whether it has been transferred
correctly.
To do this, the receiver computes a BCC from the received block and
compares it with the received BCC. If the received BCC and the computed
BCC are identical, the receiver transmits the character <ACK> for positive
acknowledgment. If the two BCCs are not identical, the data block was not
transmitted correctly. The receiver transmits the character <NAK> for
negative acknowledgment. The block must be re-transmitted. This process is
repeated up to 15 times.
If the header is acknowledged with <ACK>, the first file block can be
transmitted:
The beginning of a file block is identified by the control character <STX>. The
remaining control characters in this block are identical with the control
characters in the header. If this block is acknowledged by <ACK>, then the
next program block is transmitted. If <NAK> is transmitted, the same block
has to be re-transmitted, etc. Once the last program block has been
acknowledged by <ACK>, the transmission is terminated by the characters
<ETX> (end of text) and <EOT> (end of transmission).
The character <DC1> (XON) follows the BCC. This character is required by
many devices to explicitly request the transmission once again from the
transmitter.
The <DC1> character is not required for reading in a file in the BCC format.
The transmitter waits and only resumes data transmission when the receiver
has transmitted a positive (ACK) or negative (NAK) acknowledgment to
indicate that the receiving buffer is ready.
To disable transmission of the character <DC1>:
 Set MP_flowControl to NONE.
Example:
A file with the name PPP is to be transferred to a peripheral device (e.g.
HEIDENHAIN FE 401 Floppy Disk Unit).
Control to peripheral device
<SOH><L>PPP<A><ETB>BCC
<STX> "1st line"<ETB>BCC
...
<STX> "10th line"<ETB>BCC
<STX> "10th line"<ETB>BCC
<STX> "11th line"<ETB>BCC
...
<STX> "last line"<ETB>BCC
<ETX><EOT>
Peripheral device to control
ACK
<ACK>
...
<NAK>
<ACK>
<ACK>
...
<ACK>
HEIDENHAIN Technical Manual MANUALplus 620