Lpc2000

Herbert Demmel wrote:
> Hi,
> 
> I seem to miss something with setting up PWM5 output - the routine below 
> sometimes works, sometimes not (depending non additional code - this 
> versions below currentlly does NOT work).
> 
> Any idea what I miss to setup?
> 
> Thanks for your input.
> 
> Regards
> Herbert
> 
> #include <LPC213x.H>                    /* LPC213x definitions  */
> 
> #define TICKS_PER_US            15
> 
> void io_alarm_out(unsigned int freq)
> {

	PWMTCR = (1ul << 0) | (1ul << 1);	/* Enter reset state and force counter to zero*/

>          // match register 0 controls the cycle frequency
>          PWMMR0 = 1000000 * TICKS_PER_US / freq;
> 
>          // we want to have a duty cycle of 50% so always set PWMMR5 to 
> half of PWMMR0
>          PWMMR5 = PWMMR0 / 2;
> 
>          // enable PWM5 output
>          PWMPCR |= (0x01 << 13);

	PWMTCR = (1ul << 0) | (1ul << 3);	/* Re-enable PWM */

> }
> 
> int main(void)
> {
>          // --- PWM5 setup ---
> 
>          // Enable P0.21 to be PWM5
>          PINSEL1 |= (0x01 << 10);
>          PWMTCR = 1;             // enable PWM timer, let shadow register 
> disabled
> 
>          // reset PWM timer when PWMMR0 matches
        //  PWMMCR = 0x2;
> 
>          // gives 1000Hz
>          io_alarm_out(1000);
> 
>          while (1)
>                  ;
> }
> 

Hallo Herbert,

Mmmmh, don't you need to turn on PWM module in PCONP? Or do you let all peripherials active on
startup by default?

But bit #3 in PWMTCR enables PWM module. Description of this bit says:
"When one, PWM mode is enabled. PWM mode causes shadow registers..." (2294's datasheet, p.233)

After you have enabled PWM module (if bit #3 in PWMTCR is set) and set up a value in a PWMMRx
register you just need to set the appropriated bit in PWMLER register to take effect of new PWMMRx
value.

You do not need using PWMLER register if you hold PWM in reset state during changing PWMMRx values
(see changes above).

Try it!
  Sten

-- 
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