Digital timing using a state machine.

摘要

A digital timing generator using a state machine detects the presence of a predetermined pulse pattern at the input to generate a valid pulse output, and from the periodic repetition of the valid pulse output indicates the presence or absence of an input signal having the predetermined pulse pattern. The edges of the pulses at the input are detected (10) and the pulse widths are determined by a time duration counter (14) as being within the limits corresponding to the predetermined pulse pattern. A valid pulse counter (16) is incremented for each pulse having the proper pulse width, and when the count of the counter reaches a predetermined value a valid pulse output is indicated. The valid pulse output may be delayed before being input to a signal presence detector. Each valid pulse output restarts a time interval counter (24) and increments a valid input counter (26) so long as the time interval timer does not reach a maximum time interval. When a predetermined minimum value of the valid input counter (26) is reached, a valid input signal is indicated. Then the valid input counter (26) counts the number of consecutive times that the maximum time interval is reached without the receipt of the valid pulse output, indicating the absence of the input signal when a predetermined maximum value is reached.