Inwas: Interfacing With Asynchronous Serial Mode

Interfacing can be defined as the joining of members of a group (such as people, instruments) in such a way that they are able to function in a compatible and coordinated fashion [1]. A knowledge of interfacing fundamentals has become mandatory only recently, with the advent of digital electronics and the marketing of a wide variety of digital instruments with divergent input and output requirements. Fifteen years ago, when digital instruments were virtually unknown, the interfacing problem between two instruments was a simple one: it usually consisted of connecting a pair of wires between the instruments (and perhaps a grounded shield as well). A sound knowledge of the concepts of impedance matching, noise pickup, and ground loops was generally all that was required to interface any two instruments properly. Today, the problems of interfacing two instruments have been magnified, a direct consequence of the many new options available to the engineer or laboratory scientist. In addition to what might be called analog-to-analog interfacing, which we have just described, we now have the options of interfacing analog instruments to digital ones, digital instruments to analog ones, and most important, digital instruments to digital instruments or computers. In the fourth category, to compound the problem, there exists: 1) a variety of digital codes whereby this interfacing can be accomplished (binary, BCD, ASCII, EBCDIC, etc.