Handling with VIPA data handling blocks Manual BG41/BG42/BG43
4-44 Rev. 99/49
Passive operation:
When the procedure driver is waiting for the connection set-up and receives a character unequal to
STX, it transmits NAK. If it receives an NAK character, the procedure driver does not transmit an
answer.
If the ZVZ is transgressed at reception, an NAK is transmitted and a new connection set-up is
awaited.
If the procedure driver is not ready when receiving the STX, it transmits an NAK.
The Block Check Character (BCC byte):
In the procedure 3964R a block check character is attached to the end of the telegram for better data
protection. The BCC byte is formed by an XOR linkage through the data of the entire telegram
including the DLE/ETX.
When a BBC byte is received, which differs from the self ascertains one, an NAK instead of a DLE
is transmitted.
Initialisation conflict:
If both partners simultaneously attempt a connection set-up within the QVZ, the partner with the
lowest priority transmits a DLE and switches to receive.
DLE:
If the character DLE appears in a telegram, it is doubled by the procedure driver, i.e. DLE/DLE is
transmitted. Upon reception, double DLEs are filed as one DLE in the buffer. The combinations
DLE/ETX/BCC (only by 3964R) is regarded as the end of the telegram.
The control codes : 02h = STX
03h = ETX
10h = DLE
15h = NAK
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