User`s manual

Overview of the Serial Port
8-9
The “on” and “off” states for a data signal and for a control signal are shown
below.
The Data Pins
Most serial port devices support full-duplex communication meaning that they
can send and receive data at the same time. Therefore, separate pins are used
for transmitting and receiving data. For these devices, the TD, RD, and GND
pins are used. However, some types of serial port devices support only one-way
or half-duplex communications. For these devices, only the TD and GND pins
are used. In this guide, it is assumed that a full-duplex serial port is connected
to your device.
The TD pin carries data transmitted by a DTE to a DCE. The RD pin carries
data that is received by a DTE from a DCE.
The Control Pins
9-pin serial ports provide several control pins that:
•Signal the presence of connected devices
•Control the flow of data
The control pins include RTS and CTS, DTR and DSR, CD, and RI.
-6
Signal value (Volts)
-3
0
3
6
Data Signal Control Signal
on
off
off
on