Serial Loopback Test Plug for 9 Pin DB9 RS232 Connections

When a serial loopback test is required on a serial port - this plug is designed to help test your 9 Pin RS232 devices or use for fault finding.
This is a very handy, portable device as part of a serial port test tool kit. Can work with a serial port terminal e.g. Free SimpleTerm SE, SimpleTerm Gold or PuTTY for easy testing.

We use these in house to test a range of our devices from USB to Serials and bespoke hardware RS232 designs to make sure they go out working every time. This RS232 serial loop back tester is a 9 Pin device and all connections are within the device.

If you need to extend this device, we would advise you to use a "straight through" cable and not a "Null Modem".


The following wires are linked for loop back testing (including hanshaking signals)
i.e. 2 to 3 (TX,RX), 4 to 6 (DTR,DSR), 7 to 8 (RTS/CTS).

Has a female connection to allow you to connect to most serial devices.

Your thinking - I might buy this helpful device some other time but
how can I do a rudimentary test now...then read on...

How can I make sure my serial port is working in Windows?

To check whether or not an RS232 serial port is working, perform an RS232 loopback test by doing the following:
1) Your desktop computer or USB to serial cable port normally has a male pin connection.

Convert it by taking a female/female cable or gender changer and plugging it into the serial port.

2) Carefully take a metal paperclip or wire and cross pins 2 and 3. Look closely at the female end, the pins should be numbered.

3) Open a serial connection/session using our Free DACIO Serial Terminal Software (link below), SimpleTerm SE or PuTTY to the port you want to test.

4) When the session is open, type into it and anything you type you should see return back. When you cannot see what you are typing then the serial port loopback test has failed.

5) If the loopback test fails, make sure that the serial cable or gender changer that you are using works and that the adapter is in the correct port.

Free software (only supports COM1-COM8)
Free DACIO Serial Terminal Software

If there is a similar product you need let us know and we may stock it for you depending on demand.

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Serial Loopback Tester Plug 9 Pin DB9 RS232

  • Model No.: 1292
  • Availability: Out Of Stock
  • £3.35

  • Ex VAT: £2.79

  • 5 or more £3.02
  • 15 or more £2.95

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