Editing Counter (digital) (section)

===Pulse width modulator===

Binary counters are an essential building block in digital [[pulse width modulation|pulse width modulators]], which are commonly used to control motor speed, temperature, LED brightness, and other physical processes. These can be implemented in various ways. For example, the pulse width modulator shown below uses a single binary up-counter with synchronous reset to control both the width and frequency of output pulses:

[[File:PWM generator.jpg|450px|border|Digital pulse width modulator]]

The value stored in the PWM period register (<math>Period</math>) determines the output frequency. <math>Count</math> increments at clock frequency <math>f_{clock}</math> until it matches <math>Period</math>, which causes the identity comparator to strobe EndCycle, thus resetting the counter and starting the next output cycle. Consequently, the counter modulus is <math>Period + 1</math> and the output pulse frequency <math>f_{out} = f_{clock} / (Period + 1)</math>.

<math>Width</math> specifies the output pulse width in clock periods. The magnitude comparator asserts <math>Preview</math> while Count is less than <math>Width</math>, thus producing a pulse that starts at the beginning of the output cycle and ends when the count reaches <math>Width</math>. A flip-flop buffers <math>Preview</math> to prevent glitches from appearing on the PWM output.

The [[duty cycle]] is the percentage of PWM cycle time in which the pulse is active: <math>Duty cycle = 100 * Width / (Period + 1)</math>. For example, the following diagram shows signal timing for <math>Period = 11</math> and <math>Width = 3</math>, resulting in a 25 percent duty cycle at <math>f_{clock} / 12</math> Hertz.

[[File:PWM generator timing.jpg|450px|border|Example timing diagram for digital pulse width modulator with Period=11 and Width=3]]