Installing the Radios RLX-IFHE ♦ RadioLinx Industrial Wireless

User Manual RadioLinx® Industrial Frequency Hopping Ethernet Radios

Page 60 of 109 ProSoft Technology, Inc.

November 19, 2013

Serial Port Basics

PC communications depend primarily on serial and parallel ports to interface the

PC to the outside world. A "port" is a connection or plug-in that gives access to

the PC. The port allows the computer to communicate with devices such as

printers, input devices (serial mouse), and modems.

The serial port is more difficult to interface to than the parallel port because most

serial devices require that the serial transmission consists of characters that are

converted into a parallel format. This conversion is accomplished with a

communications controller chip, (UART: Universal Asynchronous

Receiver/Transmitter).

Two common serial interface standards are RS-232 and RS-485. The RS-232

protocol is an industry standard protocol while the RS-485 protocol is commonly

used in the industrial automation market.

There are two types of devices to which a serial-cabled device can communicate:

 DCE (Data Communications Equipment): modem, plotter, "RadioLinx Radio

Modem".

 DTE (Data Terminal Equipment): PC or terminal

Serial ports have two common connector styles:

 DB25 pin connector

 DB 9 pin connector

Today’s typical PC has one parallel port and two DTE serial ports (both are male

connectors). To connect two DTE devices to each other, the easiest (and

recommended) connection method is with a Null Modem cable (female

connectors on each end). This is commonly used as a quick and inexpensive

way to transfer files between two PCs without having to install a dedicated

network card in each PC.

Note: The RadioLinx radio modem is a DCE device.

The following table contains the pin functions for both the DB25 and the DB9

connectors:

Pin Name

Pin Number

DB9 / DB25

Function

Transmit Data (TXD)

Pin 3 / 2

Serial Data Output

Receive Data (RXD)

Pin 2 / 3

Serial Data Input

Clear-To-Send (CTS)

Pin 7 / 4

This line indicates that the modem is ready to exchange

data.

Data-Carrier-Detect

(DCD)

Pin 1 / 8

This line becomes active when the modem detects a

carrier from the modem on the other end of the phone line.

Data-Set-Ready

(DSR)

Pin 6 / 6

This tells the UART that the modem is ready to establish a

link.

Data-Terminal-Ready

(DTR)

Pin 4 / 20

This tells the modem that the UART is ready to exchange

data.

Request -To -Send

(RTS)

Pin 7 / 4

This line informs the modem that the UART is ready to

exchange data.

Ring Indicator (RI)

Pin 9 / 22

Goes active when modem detects a ringing signal