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08.89
Monitoring times
To avoid undefined conditions which can occur due to errors (mutilation of control characters
or control character sequences), monitoring periods are used. These periods are used to
initiate rerun routines if errors have occurred or to disable the connection.
TO:
On reception of DLE/STX the receiving station starts
e.g. 2s
the TO monitoring time (value configurable).
In order to permit the transmission of transmission character sequences of
different lengths, the T0 period is reset with every character received. The T0
period is reset and stopped on reception of the DLE/ETX transmission control
character. If no character arrives within the T0 monitoring time, the receiving
station moves into the basic phase.
T1:
The transmitting station or the station wishing to send starts the T1 monitoring
e.g. 3s
time by transmitting ENQ, DLE/ENQ and BCC. If within this period no valid
acknowledgement comes from the station on the other end, the latter is requested
with ENQ to send an acknowledgement (value configurable). The periods T0 and
T1 must be configured so that T0 expires before T1.
T4:
The receiving station sets the T4 monitoring time with transmission of
e.g. 24s
acknowledgement DLE0 DLE1 or NAK. If within this period a valid response of the
transmitting station does not come, the receiving station moves into the basic
phase (value configurable)
Repetitions (values configurable)
Repetitions are possible in the enquiry phase and in the text transfer phase. The number of
repetitions is configurable.
The station wishing to send transmits ENQ in the enquiry phase. If the transmitting station
receives no or a mutilated acknowledgement, the request is repeated with ENQ after expiration
of the T1 monitoring time.
If no DLE0 is received after the configured number of repetitions (e.g 4 times), the station
sends EOT and aborts the procedure.
Repetitions also are possible in the text transfer phase (value is configurable). For this
purpose, text repetitions and ENQ acknowledgement requests are added up (e.g.: one text
repetition after NAK, two acknowledgement requests ENQ after mutilated acknowledgement). If
a DLE1 is not received after the configured number of repetitions (e.g. 3 times), the
transmitting station aborts the procedure with EOT.
Data protection
In order to guarantee reliable data transmission, a character and horizontal parity protection is
used. In this way, multiple errors can be recognized. For every transmitted character a parity
bit can be included in the transmission.
In addition, the transmitted text is saved on a block basis. For this purpose, a logical "XOR" is
generated covering the message frame from ID to ETX inclusively. The character obtained in
this way is the block check character (BCC). The block check function is set to zero for STX.
In the receiving station, BCC is also computed and compared with the transmitted BCC.
© Siemens AG 1989 All Rights Reserved
SINUMERIK 840/880 (PJ)
6FC5 197-0AB20-0BP0
9 Appendix
9.2 LSV2 procedure
9–11
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