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Serial communication protocols
3964(R) > Basics 3964(R)
5.4 3964(R)
5.4.1 Basics 3964(R)
Mode of operation
Procedure
Timeout times
Passive operation
68
The 3964(R) procedure controls the data transfer of a point-to-point link between the CP
and a communication partner. The procedure adds control characters to the telegram
data during data transfer. These control characters may be used by the communication
partner to verify the complete and error free receipt.
The procedure employs the following control characters:
n
STX Start of Text
DLE Data Link Escape
n
n
ETX End of Text
n
BCC Block Check Character (only for 3964R)
n
NAK Negative Acknowledge
When a DLE is transferred as part of the information it is repeated to dis-
tinguish between data characters and DLE control characters that are
used to establish and to terminate the connection (DLE duplication). The
DLE duplication is reversed in the receiving station. The 3964(R) proce-
dure requires that a lower priority is assigned to the communication
partner. When communication partners issue simultaneous send com-
mands the station with the lower priority will delay its send command.
You can maximally transfer 250byte per telegram.
The QVZ is monitored between STX and DLE and between BCC and DLE. ZVZ is moni-
tored for the entire period of receiving the telegram. When the QVZ expires after an STX,
the STX is repeated. This process is repeated 5 times after which the attempt to establish
a connection is terminated by the transmission of a NAK. The same sequence is com-
pleted when a NAK or any other character follows an STX. When the QVZ expires after a
telegram (following the BCC-byte) or when a character other than DLE is received the
attempt to establish the connection and the telegram are repeated. This process is also
repeated 5 times after which a NAK is transmitted and the attempt is terminated.
When the procedure driver is expecting a connection request and it receives a character
that is not equal to STX it will transmit a NAK. The driver does not respond with an
answer to the reception of a NAK. When the ZVZ is exceeded at reception, a NAK is sent
and it is waited for a new connection. When the driver is not ready yet at reception of the
STX, it sends a NAK.
VIPA System SLIO
HB300 | CP | 040-1CA00 | en | 18-28
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