Pulse Width Modulators
The default BIOS configuration table defines four dedicated PWM outputs as PWM_0, PWM_1, PWM_2, and PWM_3, each with programmable frequency and duty cycle.
The table below shows examples of hardware (register) based PWM programming.
The PWM variables that control frequency and duty cycle are controlled by the BASE_UNIT_INT, BASE_UNIT_FRAC, and ON_TIME_DIVISOR register settings and the following equations:
PWM frequency formula:
PWM duty cycle formula:
Note: Consult specific operating system documents if manipulating PWM settings at the OS level. |
PWM Programming examples
Item | Example 1 | Example 2 | Example 3 |
Integer part of BASE_UNIT_INT (bits 29:22) | 0000_0000b | 0000_0000b | 0000_0000b |
Fractional part of BASE_UNIT_FRAC (bits 21:8) | 00_0100_0000_0000b | 00_0010_0000_0000b | 00_0001_0000_0000b |
Decimal base unit value | 0.0625 | 0.03125 | 0.015625 |
ON_TIME_DIVISOR (bits 7:0) | 0000_1000b | 0000_0100b | 0000_0001b |
Base unit type | fractional | fractional | fractional |
PWM frequency (Hz) | 4,688 | 2,344 | 1,172 |
PWM period (usec) | 213 | 427 | 853 |
Duty cycle | 50% | 50% | 50% |
See also: Pulse Width Modulators in the Expansion Board Hardware Datasheet.