Using the HC12 PWM

  1. Choose 8-bit mode (PWCLK 7:6 = 00)
  2. Choose left-aligned (PWCTL 3 = 0)
  3. Choose polarity = 1 (PPOL 3:0 = 1111)
  4. Select clock mode in PWPOL: PCLKx = 0 for $2^N$,
    PCLKx = 1 for $2^{(N+1)} \times (M+1)$,

  5. Select $N$ in PWCLK register: PCKA 2:0 for channels 1, 0; PCKB 2:0 for channels 3, 2.

  6. If PCLKx = 1, select $M$: PWSCAL0 7:0 = $M$ for channels 1, 0; PWSCAL1 7:0 = $M$ for channels 3, 2.

  7. Select PWPERx, normally between 200 and 255.

  8. Enable desired PWM channels: PWEN 3:0.

  9. Select PWDTYx, normally between 0 and PWPERx. Then

    \begin{displaymath}{\rm Duty\ Cycle\ x} = \frac{{\tt PWDTYx}+1}{{\tt PWPERx}+1} \times 100 \%\end{displaymath}

    Change duty cycle to control speed of motor or intensity of light, etc.

  10. For 0% duty cycle, choose PWDTYx = 0xFF.


Bill Rison
2001-03-05