What Is RS-232 Port DB9 DB25 Connector For Headend Equipments



There are lot of Digital Headend Equipments in which we see RS-232 serial port. These devices are STBs , Decoders and Servers etc. This port can be 3-PIN , 9-PIN and even 25-PIN.

In this article we will cover what is RS-232 port , RS-232 Port working and functions and why it is used. Also its upgraded version.

What Is RS-232


RS-232 is a standard was introduced in 1960. It is used for transmission of data by serial communication. It defines the connection between DTE and DCE. DTE stands for Data Terminal Equipment while DCE stands for Data Communication Equipment. Where Data Terminal Equipemnt can be Computer and Data Communication Equipment can be Modem, printer and Set Top Box.

RS232 cable length can be maximum of 15 meter or 50ft. It has lower data transmission speed. While other standards like RS 422 , RS 485 and Ethernet have higher data transmission speed.

There are basically two types of RS-232 Ports like 9-PIN RS-232 Port and 25-PIN RS-232 Port. The 9-PIN RS232 connector is known as DB9 Connector while 25-PIN RS232 connector is known as DB25 connector.

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3 PIN RS232 To 9 PIN RS 232 Cable

How Does RS-232 Works ?

male female rs232

As shown above in the figure there is 5 PIN RS232 Connectors male and female both. The sequence of PIN numbers is mentioned above in diagram.  Each of this PIN is responsible for different function.

Let us now understand the functions of 5 PIN Male RS232 Connector,

PIN Number
DTE  (Computer)
1DCDData Carrier DetectInput
2RXDReceived DataInput
3TXDTransmitted DataOutput
4DTRData Terminal ReadyOutput
6DSRData Set ReadyInput
7RTSRequest To SendOutput
8CTSClear To SendInput
9RIRing IndicatorInput

PIN number 1, 2 and 3 are very important PINs because 1 is used to detect the data carrier . 2 is used to receive the data while 3 is used for transmission of data.

Lets have a look at functions of 25-PIN RS-232 Connector,

25 pin rs232
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What Are Applications Of RS 232 ?

It is used in connecting printer to computer

It is used in Connecting monitor to CPU.

It is used in connecting Set Top Box with Computer to download the new software , firmware or release in STB. Generally we see 3-PIN RS 232 slot in STBs to connect with Computer. For this reason we need to use cable mentioned below,

as you can see in the image 3 pin RS232 will connect in the STB while other port will connect directly into the PC. If in case your PC is not having this 5-PIN RS232 port jack then you need to purchase 5-PIN male RS232 to USB cable.


A 9-PIN RS232 cable is generally used in connecting switches, STBs, printers and monitors to computer or servers. Technically its cable length depends upon the baud rate. Now a days USB to RS232 cable are used to connect old devices to PC. A USB port have removed the use of RS232 port.

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