In this second part we concentrate on software. We take a closer look at the IOtest program presented in the first article and use simple program examples in Visual Basic to control a model traffic light and a clock generator.In the first article in this series we introduced the IOtest program. The majority of readers with some programming experience will be interested in how we access the serial interface using Visual Basic. Here we will use a library of program subroutines called PORT.DLL written by H.-J.Berndt. This DLL file is available from the Free Downloads section of the Elektor Electronics website. For those with no access to the Internet, the file is also found on the diskette containing the course software.