RS-232 Mini Tester

How to know which RS-232 data lines are active?

The RS-232 Mini Tester is an efficient device to connect in series with any RS-232 interface for testing a serial (RS-232) link. An example of how an RS-232 mini tester looks like is shown in figure-1 below.


Figure-1: RS-232 Mini Tester

The RS-232 Mini Tester is installed between host PC and an intended equipment in order to test the serial link for any failures. As can be observed in figure-1, the mini tester has 7 bi-colour (red and green) LED’s (Light Emitting Diodes) which indicate the logic states for respective data lines. The colour of LED indicates Negative or Positive voltage, red meaning negative and green meaning positive voltage.

For example, green colour on TD implies positive voltage for ‘Transmit Data’ and red colour implies negative voltage for TD, Green colour on RD implies positive voltage for ‘Receive Data’ and red colour implies negative voltage for RD.

Seven LED’s indicate the status of the following data lines;


TD —- Transmit Data

RD —- Receive Data

RTS —- Request To Send

CTS —- Clear To Send

DSR —- Data Set Ready

CD —- Carrier Detect

DTR —- Data Terminal Ready


Links to the stores where these RS-232 Mini Testers can be bought:

1. B&B Electronics:

RS-232 Mini Tester from B&B Electronics online at

B&B Electronics Mfg. Co.
707 Dayton Road
P.O. Box 1040
Ottawa, IL 61350


2. Triangle LLC:

RS-232 Mini Tester from Triangle LLC online at LLC
18735 East Colonial Drive
Suite 112
Orlando, Florida 32820


3. CNC Speciality Store LLC:

RS-232 Mini Tester from CNC Speciality Store LLC online at

CNC Specialty Store LLC
1318 Colonial Drive
Watertown, WI 53098


4. CWC Groups:

RS-232 Mini Tester from CWC Groups online at

1290 E. Acacia Street
Ontario, California 91761


5. Newark/element14 [Premier Farnell Canada Limited]

TS500A-R2 – DB9 Pocke Tester at Newar/Element14 online at

Premier Farnell Canada Limited
c/o T27537 PO Box 4275
Postal Station “A”
Toronto, ON
M5W 5V8