User manual

IEC61131 User and Reference Manual
April 22, 2008
33
Figure 6: DNP Configuration (Flow Control) Dialog Box
The RTS/CTS Flow Control grouping contains two mutually exclusive options, Use
Hardware Control Lines and Use CTS Delay Time. These options enable the driver to
communicate over radio or leased-line networks using modems that require RTS/CTS
handshaking.
The Use Hardware Control Lines option specifies a half-duplex connection requiring the
use of the Request to Send (RTS) and Clear to Send (CTS) hardware control lines to control
the flow of data. This selection is used with radios and dedicated telephone line modems.
The driver turns on the RTS signal when it wants to transmit data. The modem or other
device then turns on CTS when it is ready to transmit. The driver transmits the data, and
then turns off the RTS signal. This selection is mutually exclusive of the Use CTS Delay
Time selection described below. This is the default selection.
The Use CTS Delay Time option is selected if the device cannot generate a CTS signal.
The driver will assert RTS then wait the specified Delay Time, in milliseconds, before
proceeding. This option is mutually exclusive with the Use Hardware Control Lines selection
described above.
The Delay Time parameter sets the time in milliseconds that the driver will wait after
asserting RTS before proceeding. The value of this field must be smaller than the Time Out
value set in the General parameters dialog. For example, if the Timeout value is set to 3
seconds, the CTS Delay Time can be set to 2999 milliseconds or less. The minimum value
for this field is 0 milliseconds. The value is initially set to 0 by default.