HEIDENHAIN TNC 335 Technical Manual - Manual (Page 526)

8/95
TNC 360 2 TNC data interfaces 8-19
If the two BCCs are not identical, the receiver sends character <NAK> (= Not AcKnowledged), i.e.
the data block has been incorrectly transferred and the same block must be sent again. This process
is repeated up to three times. An error message ("TRANSFERRED DATA INCORRECT N") is
displayed, and transfer is aborted.
If, however, this header is acknowledged with <ACK>, the first data block can be transmitted:
<STX>0 BEGIN PGM 1 MM <ETB> BCC <DC1>.
The start of a data block is always indicated by control character <STX>. The other control
characters in this block are identical to the control characters of the header.
If the block is acknowledged with <ACK>, the next program block is sent. In the event of a <NAK>,
the same block must be repeated, and so on...
If the last program block has been sent successfully (acknowledged with <ACK>), transmission
ends with characters <ETX> (End of Text) and <EOT> (End of Transmission).
Table of control characters:
Character Meaning Description
SOH Start of Header SOH indicates the start of the
transfer of the data header. The
header is a sequence of characters
which contains the program number
and information concerning the type
of program and transmission mode.
STX Start of Text STX indicates the start of the
program block.
ETB End of Text Block ETB ends a data transfer block. The
character following ETB is used for
data checking (BCC).
DC1 Start data transfer (XON) DC1 starts data transfer after a stop.
DC3 Stop data transfer (XOFF) DC3 stops data transfer.
ETX End of Text ETX is sent at the end of the
program.
EOT End of Transmission EOT ends data transmission and
produces the quiescent state. This
character is sent by the TNC at the
end of program input, and as an error
to external devices
ACK ACKnowledged ACK is sent by receiver when a data
block has transferred without error.
NAK Not AcKnowledged NAK is sent by the receiver when a
data block has transferred
incorrectly. The transmitter must
transmit the data block again.