RS-232 Test Software

RS stands for recommended standard. In the 60's a standards committee now known as the Electronic Industries Association developed an interface to connect computer terminals to modems. Over the years this has been updated: the most commonly used version of the standard is RS232C (sometimes known as EIA232); the most recent is RS232E. The standard defines the electrical and mechanical characteristics of the connection - including the function of the signals and handshake pins, the voltage levels and maximum bit rate.


If RS232 is a standard why can't I just use a standard lead to connect together two RS232 ports and expect them to talk to one another? That's a good question. The answer is that the RS232 standard was created for just one specific situation and the difficulties come when it is used for something else. The standard was defined to connect computers to modems. Any other use is outside of the standard.


he standard defines how computers (it calls them Data Terminal Equipment or DTEs) connect to modems (it calls them Data Communication Equipment or DCEs). The standard says that computers should be fitted with a 25 way plug whilst modems should have a 25 way D socket. The interconnecting lead between a computer and a modem should be simply pin1-pin1, pin2-pin2, etc. The main signals and their direction of flow are described below. It is important to note that a signal which is an output from a computer is an input to a modem and vice versa. This means that you can never tell from the signal name alone whether it is an input or an output from a particular piece of equipment. Also, instead of being a DCE device, a data acquisition device might be configured as DTE. In this case you need an adaptor or the RS232 cable wired differently to normal. When the PC is connected to a DTE instrument - called a null modem arrangement - some of the cable wires must cross over.


RS-232 Test Software will help you to monitor and analyze serial port communication.