User`s manual

8 Serial Port I/O
8-56
Using Control Pins
As described in “Serial Port Signals and Pin Assignments” on page 8-6, 9-pin
serial ports include six control pins. These control pins allow you to:
•Signal the presence of connected devices
•Control the flow of data
The properties associated with the serial port control pins are given below.
Signaling the Presence of Connected Devices
DTE’s and DCE’s often use the CD, DSR, RI, and DTR pins to indicate whether
a connection is established between serial port devices. Once the connection is
established, you can begin to write or read data.
You can monitor the state of the CD, DSR, and RI pins with the
PinStatus
property. You can specify or monitor the state of the DTR pin with the
DataTerminalReady property.
The following example illustrates how these pins are used when two modems
are connected to each other.
Example: Connecting Two Modems
This example connects two modems to each other via the same computer, and
illustrates how you can monitor the communication status for the
computer-modem connections, and for the modem-modem connection. The first
modem is connected to COM1, while the second modem is connected to COM2.
Table 8-11: Control Pin Properties
Property Name Description
DataTerminalReady
Specify the state of the DTR pin
FlowControl Specify the data flow control method to use
PinStatus Indicate the state of the CD, CTS, DSR, and RI pins
RequestToSend Specify the state of the RTS pin