Defensive software programming with embedded microcontrollers

Microcontrollers today are being designed in more and more electronic applications, from automotive, industrial and consumer markets. This growth has been driven by the decrease in silicon transistor geometries, that have in turn reduced dramatically the cost of these complex designs. With decrease in geometries of silicon transistors in metal-oxide semiconductors, electromagnetic compatibility (EMC) has become a major consideration when designing such devices in their end application. EMC has two aspects: immunity and emissions. Within embedded microcontrollers, software is not normally seen to have an effect on emissions, as emissions are caused mainly by the harmonics of the internal clock of the CPU, and the fast switching current caused by multiple gates within the microcontroller. The external PCB further amplifies these noise signals to unacceptable levels if the layout design has no EMC considerations. In most cases the software cannot adversely affect these intrinsic events. Immunity performance can be increased by software within microcontrollers and the paper gives an introduction on techniques used. EMC noise can cause malfunction to any circuit or part of a circuit within the microcontroller. Electromagnetic noise has two forms-radiation and conduction. Conducted electromagnetic noise will travel from the perimeter of the die inwards, and may affect input/output ports first, before affecting circuits within the centre of the die. Radiated noise by its nature is expected to have a more random effect, but generally emitted noise becomes conductive on the PCB tracks.