State of the DTR pin
You can configure DataTerminalReady to be on or off. If DataTerminalReady is on, the Data Terminal Ready (DTR) pin is asserted. If DataTerminalReady is off, the DTR pin is unasserted.
In normal usage, the DTR and Data Set Ready (DSR) pins work together, and are used to signal if devices are connected and powered. However, there is nothing in the RS-232 standard that states the DTR pin must be used in any specific way. For example, DTR and DSR might be used for handshaking. You should refer to your device documentation to determine its specific pin behavior.
You can return the value of the DSR pin with the PinStatus property. Handshaking is described in Controlling the Flow of Data: Handshaking.