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Handshaking
8 – 24
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, then the error message "Transferred data
incorrect E" is output. The transmission is aborted.
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. With <NAK>, 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 <DC1> character in the EXT1, EXT2 and EXT3
modes:
7 7 7 7
Set MP5020 bit 3 = 0.
Example:
To read out a pallet file with the name PPP to a peripheral device (e.g. FE 401).
TNC to peripheral
<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 to TNC
ACK
<ACK>
...
<NAK>
<ACK>
<ACK>
...
<ACK>
HEIDENHAIN Technical Manual TNC 426, TNC 430
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