Real World Instrumentation with Python

Serial Interfaces

The three most common types of serial interfaces you are likely to encounter when dealing with instrumentation device interfaces are RS-232, RS-485, and USB. The RS-232 and RS-485 standards were originally given the RS (Recommended Standard) designation by the Electronic Industries Alliance (EIA). When the maintaining organization changed its name the prefix changed as well, first to EIA-232 and finally to TIA-232. The standards are currently revised and maintained by the Telecommunications Industry Association, but since the RS nomenclature is so deeply ingrained in the history of electronics engineering and telecommunications, it has refused to go away. In this book I will use the RS-232 and RS-485 names for these standards.

USB interfaces have become very common over the past decade, to the point where USB has largely supplanted the RS-232 interface once found on just about every PC. Only desktop or rack-mounted PCs still provide serial interfaces (and even some of the thin rack-mount units have done away with them). The latest models of notebooks and so-called netbook computers now have only USB ports.

There are a variety of different types of special-purpose, high-reliability serial interfaces used in specific applications. These include CAN (Controller Area Network), FieldBus, and Profibus. The MIL-STD-1553 serial bus found in military applications and some avionics is yet another example. These are specialized interfaces that are not often encountered outside ...