Re: strange tpu pwm problem

Is it possible that your outputs are configured for low power drive and 
that the signal is just not able to climb to logic 1 below 6% high time?

fatih_lokumcu wrote:

> Hello,
> I have a strange problem. I use the tpu pwm function to
> produce a 20 hz pwm which varies between %5 and %10 duty cycles for
> servo control.
> I have metrowerks mpc5xx edition 8.0 with phycore 565 board.
> It works fine between %6 and %10 duty cycles but all of the lower
> duty cycle commands lead to a %0 duty cycle. (which has a low time of
> 250 ns.)
>
> Here is my code:
>
> UINT16 period ;
> UINT16 hightime;
> struct TPU3_tag *tpub = &TPU_B;
>
> void InitServo(void) {
>       period = 35000;
>       hightime = 2232;
> tpu_pwm_init(tpua,0,TPU_PRIORITY_HIGH,period,hightime,TPU_PWM_TCR1);
>
> }
>
> when TCR1 is used with  PSCK = 0 it it divides the 56 mhz clock by 32
> and period value of 35000 makes the wave 20 hz. So to produce the pwm
> between 1ms and 2ms duty cycle hightime must be between 3500 and 1750.
> The code above works fine until the hightime is set below 2232. I
> tried to change the hightime with tpu_pwm_update function but nothing
> has changed. There is no scheduling problem since no other tpu
> funtion is used.
> Also, the same code works with phycore mpc555 (with period = 25000
> for 40 mhz of course.) without any problem.
>
> Is there any explaination for this?
>
> Thanks in advance,
>
> Fatih Lokumcu.
>
>
>
>
>
>
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-- 
Eric McRae, Electro-Logic Machines, Inc.
511 Root St., Port Townsend WA, 98368
Phone/Fax: 360.379.0969, http://www.elmi.com



-----------------------------------------------------------
To learn more about Freescale Microcontrollers, please visit
http://www.freescale.com/mcu


 
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