Lpc2000

> I still can't get it running. Karl showed me the way to understand 
> the docu - at least I felt like understanding it...
> Current code status:
> 
> //testing PWM4
>   PINSEL0 |= 0x20000;   // select pin 0.08 PWM4 function
>   
>   PWM_PR  = 0x0000;          // max prescale counter value
>   PWM_MCR = 0x0002;         // reset TC when PWMMR0 matches
>   PWM_PCR = 0x7E00;         // enable all PWM just to get the right one
>   PWM_TCR = 0x000A;      // reset TC counter (not yet needed?!)
>   
>   PWM_MR0 = 0x0400;          // match register 0 trigger value
>   PWM_LER |= BIT0;
>   
>   PWM_MR4 = 0x0150;      // match register 4 trigger value
>   PWM_LER |= BIT4;            
>   
>   PWM_TCR = 0x0009;          // set the TC counter and enable the PWMs
> 
> But still getting the single 88.64 ms pulse.
> Any idea?
> 
> Cheers, Kurt.

Hi Kurt,

I think the main problem is that you have to wait until you get the Match _before_
the PWM cycle is actually written. This would explain why you only get a single pulse.

Follow this procedure I use :

/* Setting the PWM cycle */
/*******************/
PWMTCR = 0x0B;                // Hold TC in reset while altering Cycle
PWMMR0 = CYCLE;             // Write the new PWM period
PWMMCR = 0x01;               // Allow the INT flag for MR0
PWMTCR = 0x09;                // Restart PWM
PWMIR |= 0x01;                 // Reset MR0 Int flag
PWMLER = 0x01;                // Enable PWM0 latch
while ( ! (PWMIR & 0x01));  // Wait for match -> new cycle complete
PWMMCR = 0;                    // Disable MR0 Int flagging

/* Setting , for example, PWM5 */
/***********************/
PWMMR5 = DUTY;              // write duty cycle
PWMLER = 0x20;                // enable PWM5 Latch

Obviously CYCLE is the total PWM cycle and PERIOD makes the
PWM's dutycycle as = DUTY / CYCLE

So if you eg. set CYCLE to 1000 and DUTY to 150 you would get a 15% dutycycle
with a frequency of PCLK / 1000 (cycle), providing Prescaler is set to ONE (=0).

There might be better ways of doing this, but this way ensures you wait long enough 
for the PWM period cycle to update, but no longer than necessary......

B rgds and good luck,
Kris


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