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08.89
Data exchange process
The procedure can be divided into three phases:
•
Enquiry phase,
•
Text transfer phase and
•
Completion phase.
Enquiry phase
MA
SL
ENQ
DLE0
MA : Master station = Text transmitting station
SL : Slave station = Text receiving station
Enquiry phase
At the beginning of the first phase, the enquiry phase, both stations are in a neutral state. If a
station wishes to send, it requests the station on the other end to receive text by transmitting
the ENQ control character and waits for the DLE 0 control character sequence. If the other
station sends this character sequence and it is received by the station wishing to send without
error, the station wishing to send moves into the text transfer phase. The figure on the next
page shows the enquiry phase and also covers all possible error conditions. If the station
wishing to send receives a character sequence containing errors, it ignores these characters.
Only after monitoring timeout, the station recognizes the error condition and repeats the ENQ
enquiry.
If the station wishing to send receives a negative acknowledgement NAK, the station on the
other end is not ready to receive text, and the station wishing to send aborts the procedure
with EOT. Upon receipt of the DLE 1 character sequence, it is assumed that the other station
end is still in the completion phase. Then the station wishing to send sends EOT (thus causing
the station on the other end to return to the initial state) and, with ENQ, requests it again to
receive text. By sending STX, the station wishing to send moves into the text transfer phase
and becomes a text transmitting station. By receiving STX, the other station also moves into
the text transfer phase and becomes a receiving station.
© Siemens AG 1989 All Rights Reserved
SINUMERIK 840/880 (PJ)
Text transfer phase
MA
DLE STX Text DLE ETX BCC
6FC5 197-0AB20-0BP0
9 Appendix
9.2 LSV2 procedure
Com.ph
SL
MA
DLE1
EOT
9–7
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