Skip to content

Latest commit

 

History

History
54 lines (42 loc) · 2.22 KB

pwm.md

File metadata and controls

54 lines (42 loc) · 2.22 KB
Raw

Pulse width modulation (PWM)

Pulse width modulation allows you to create a block wave with a certain duty cycle. It is useful for use cases like dimming LEDs.

             <--> pulse-width
___          ____          ____
   |        |    |        |    |           duty-cycle = pulse-width / period
   |________|    |________|    |______
             <--period--->

There are 12 PWM channels.

Each channel consists of a free-running 8-bit counter with two configurable comparators. The period comparator resets the counter value back to zero once it reaches a user-configured top value. This sets the period (number of cycles between rising-edges of pulses) of the output waveform. The pulse width comparator changes the channel output from high to low when the counter value surpasses a user-configured pulse width value. This sets the pulse width (number of cycles the output spends high) of the output waveform.

Each channel has a 64-bit section in the address space for configuration. Not every channel output has yet been connected to an external pin.

Offset PWM channel External pin
0x00 Channel 0 mikroBUS PWM
0x08 Channel 1 N/C
0x10 Channel 2 N/C
0x18 Channel 3 N/C
0x20 Channel 4 N/C
0x28 Channel 5 N/C
0x30 Channel 6 N/C
0x38 Channel 7 N/C
0x40 Channel 8 N/C
0x48 Channel 9 N/C
0x50 Channel 10 N/C
0x58 Channel 11 N/C

Config

For each channel, there is a 32-bit register defining the pulse width and another 32-bit register above it defining how long the complete wave is (counter top). These registers are write-only, and will return a value of zero if read.

Offset Description Read/Write
0x0 Pulse width Write-only
0x4 Counter top Write-only

A channel is enabled by setting an non-zero counter top value.

To generate an always-low signal, set a counter top value of zero. To generate an always-high signal, set a pulse-width value greater than the (non-zero) counter top value.