HEIDENHAIN TNC 426 PB

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8 – 24 HEIDENHAIN Technical Manual TNC 426, TNC 430

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).

Handshaking 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 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 Peripheral to TNC

<SOH><L>PPP<A><ETB>BCC ACK

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HEIDENHAIN TNC 426 PB - Handshaking