HEIDENHAIN TNC 407 (243 020) Technical Manual - Manual (Page 684)

01.98
TNC 407/TNC 415/TNC 425 2 TNC data interfaces 8-37
In this example program "15" that has been written in HEIDENHAIN dialog ("H") is downloaded
across the data interface (E"). A parity bit is also generated for the BCC (with even parity the BCC
parity bit in this example is assigned significance "1").
The character is transmitted after the BCC. This character (XON) is necessary for certain
devices in order to explicitly request an answer from them and to reactivate the transfer.
The transfer of the character can be suppressed in modes EXT1, EXT2 and EXT3 by setting
bit 3 in machine parameter 5020.X ("Transmission stop by DC3") to zero (see section "Freely
configurable interfaces").
The character is not required when reading in a file in the format with BCC.
At the end of every block the receiver checks that it has 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 (= positive
checkback), i.e. the data block has been transmitted without error.
If the two BCCs are not identical then the receiver transmits the character (= negative
checkback), i.e. the data block was not transmitted correctly and must be re-transmitted. This
process is repeated three times, then the error message ("TRANSFERRED DATA INCORRECT E {XE
"TRANSFERRED DATA INCORRECT E") is output and the transfer is aborted.
If the header is acknowledged with however the first file block can be transmitted:
0 BEGIN PGM 1 MM BCC
The beginning of a data block is always identified by the control character . The other control
characters in this block are identical with the control characters in the header.
If the block is acknowledged by then the next program block is transmitted, with the
same block has to be re-transmitted etc.
Once the last program block has transferred successfully (acknowledged by ) the transmission
is terminated by the characters (end of text) and (end of transmission).