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3 Interface Modules
3.3.3 XON/XOFF procedure
3.3.3.3
Signal chart for the XON/XOFF procedure
3.3.3.3.1 Read data
DTR
DSR
CTS
RTS
RxD
TxD
("Data Start" command)
DTR is activated after initialization of the interface.
The pin assignments refer to the receiver in the previous figure (EI = End identifier)
After initialization of the interface, the DTR signal line is activated. After the command "Data
Start" has been issued, the station transmits the XON control character.
If no free receiving scratch is available to the driver, it transmits the XOFF control character.
Under these circumstances, however, the driver is still able to receive and buffer up to ten
characters until a free scratch is available again. The driver checks every 100 ms whether a
new scratch is available. As soon as the receiving scratch is free, the buffered characters are
copied into the scratch and an XON character is sent. The station is now again ready to
receive.
A receiving job is terminated if the end criterion is met. The driver then terminates the
receiving scratch and passes it on to the higher-level buffer manager of the device
management level. Receiving jobs where the end criterion is not complied with are rejected by
the driver.
The end identifiers for the input direction can be configured by the user who can decide
whether to assign no, one or two end identifiers.
3–22
Data
T
m
XON
XOFF
© Siemens AG 1989 All Rights Reserved
Data
(EI)
XON
XOFF
(...) Depending on configuration
6FC5 197-0AB20-0BP0
SINUMERIK 840/880 (PJ)
06.91
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