software PWM

[bleumers_j]

Posted on June 24, 2004 at 02:25

software PWM

[bleumers_j]

Posted on June 22, 2004 at 07:36

Hi,

I'm trying to generate code in a cheap ST7LITE09 with 3 sofware PWM's. But it doesn't work and i can't find the mistake.

Any idea's.

This is the code:

#include ''Io7FLite0.h'' // ST7Flite0 memory and registers mapping

#include ''lib_bits.h'' // Predifined libraries working at bit level

#include ''bitdef.h'' // This file defines the names of the bits

int tijd,teller;

int pwm1,pwm2,pwm3;

void main(void)

{

LTCSR=0x10;

ATCSR=0x12;

PBDDR=0x07;

PBOR=0x07;

PBDR=0x00;

teller = 0;

pwm1 = 125; // write testvalue into pwm (50% dutycycle)

pwm2 = 125;

pwm3 = 125;

_asm(''rim'');

while(0)

{

}

}

@interrupt void AR_timer(void)

{

if (teller == 0)

{

SetBit(PBDR,0);

SetBit(PBDR,1);

SetBit(PBDR,2);

}

if (teller == pwm1)

ClrBit(PBDR,0);

if (teller == pwm2)

ClrBit(PBDR,1);

if (teller == pwm3)

ClrBit(PBDR,2);

teller++;

tijd = ATCSR; // Reset timer flag

}

Thanks in advance!

[sjo]

Posted on June 22, 2004 at 10:14

Below is a simple 3 channel pwm - freq 192Hz 0-100Duty.

Alter the g_cCounter reload value to adjust resolution/speed, eg.

change reload g_cCounter with 20 will alter pwm freq to approx 960Hz, the resolution will be much less - 20 steps rather than 100.

Adjust to suit your project.

unsigned char g_cCounter;

counter for motor pwm

volatile unsigned char g_cPwms[3]; // Motor PWM speeds

void main(void)

{

g_cPwms[0] = 50;

g_cPwms[1] = 30;

g_cPwms[2] = 50;

g_cCounter = 0;

ATR = 0xE5F;

ATCSR = 0x12;

PBDDR=0x07;

PBOR=0x07;

PBDR=0x00;

rim();

while(1);

}

@interrupt void AR_timer(void)

{

if( g_cCounter >= g_cPwms[0] )

ClrBit( PBDR, 0 );

else

SetBit( PBDR, 0 );

if( g_cCounter >= g_cPwms[1] )

ClrBit( PBDR, 1 );

else

SetBit( PBDR, 1 );

if( g_cCounter >= g_cPwms[2] )

ClrBit( PBDR, 2 );

else

SetBit( PBDR, 2 );

if( ++g_cCounter >= 100 )

g_cCounter = 0;

ATCSR; // clear OVF flag

}

One point to remember as this device does not have nested interrupts, the ar timer interrupt is low priority - any other interrupt will seriously interfere with the software pwm above.

Regards

sjo

[ This message was edited by: sjo on 22-06-2004 13:49 ]

[luca239955_st]

Posted on June 22, 2004 at 12:23

one important difference between sjo's code and yours (although I'm not sure that's where your problem is coming from) is the use of the ''volatile'' keyword. More details at http://www.stmcu.com/forums-cat-1665-1.html

Regards,

Luca

[ This message was edited by: _luca on 22-06-2004 15:53 ]

[bleumers_j]

Posted on June 23, 2004 at 05:44

Hi,

I have changed my code in the interrupt module to the code Sjo gave, and it works!

I think the problem was that when i write 'teller++' and teller = 255, it does not become 0 (as i thought), but it stays

I'm not sure this is the cause of the trouble, but i'll experiment with it when i have more time.

Thanks for your help!!!

[huaer2000]

Posted on June 24, 2004 at 02:25

sjo,

If I want to make the PWM frequency higher to 10K/20K, if your software can

do this?

best regards

mcuinterest