4. Time and event management

4.1 Principles

Any industrial control system must be able to maintain a clock that accurately indicates the current time, to generate signals of given period and duration, to count the number of pulses of an external signal, and to know exactly when an event has taken place.

Microcontrollers generally feature a free counter (e.g. a 16-bit counter) which increments its value on each edge of a clock signal. When the counter passes from its maximum value to zero, an interrupt is generated. The interrupt routine associated with this interrupt can maintain a higher-resolution software counter (e.g. 32 or 64 bits), so that an absolute time value is available at all times.

To generate microcontroller-programmable duration signals, the program...