LPC2148 Pulse width demultiplexer using CAP0.0

Noel Le Moult Guest #1183238
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Hello,

I have an Logomatic-v23 board from Sparkfun electronics. I want to use 
an ADXL213AE accelerometer.

The ADXL send his PWM output value and i want to capture it using the 
CAP0.0 input of the LPC2148. Unfortunately I have tried the following 
code and it don't want to acquire the value.

Initialization :
1
//Enable Interrupts

2
VPBDIV=1;    // Set PCLK equal to the System Clock

3
VICIntSelect = ~(UART1_INT | RTC_INT | TIMER0_INT);

4
VICVectCntl0 = 0x20 | 7;      //Set up the UART1 interrupt

5
VICVectAddr0 = (unsigned int)ISR_RxData1;

6
VICVectCntl1 = 0x20 | 13;      //Set up the RTC interrupt

7
VICVectAddr1 = (unsigned int)ISR_RTC;

8
VICVectCntl2 = 0x20 | 4;      //Timer 0 Interrupt

9
VICVectAddr2 = (unsigned int)ISR_Timer0;

10


11
//TIMER0 setup

12
T0TCR = 0x02;       // TIMER0 Disable; reset T0TC & T0PC

13
T0PR = 0x00000000;  // Reset T0PR

14
T0CTCR = 0x00;      // Timer Mode: every rising PCLK edge

15
T0CCR = 0x06;       // Capture on CAPn.0 falling edge and Interrupt on CAPn.0 event

1
static void ISR_Timer0(void)

2
{

3
    //Interrupt Code Here

4
    T0TCR = 0x02;       // TIMER0 Disable; reset T0TC & T0PC

5
    T0PR = 0x00000000;  // Reset T0PR

6
  

7
    YPacc = T0CR0;     //Get accelerometer captured value

8
    

9
    T0IR = 0xFF;       //Clear the timer interrupt

10
    T0TCR = 0x01;      // TIMER0 Enable 

11
    VICVectAddr =0;    //Update the VIC priorities

12
}


Main code :
1
rprintf_devopen(putc_serial0); //Init rprintf

2
rprintf("ADXL2148 Accelerometer Yp raw data :\n\r");

3


4
VICIntEnable |= TIMER0_INT;  //Enable Timer0 Interrupts

5
T0TCR = 0x01;       // TIMER0 Enable 

6


7
while( 1 )

8
{

9
    rprintf("T0CR0:%i\n\r",T0TC);

10
}


Output on Hyperterminal :
1
ADXL2148 Accelerometer Yp raw data :

2
T0CR0:369396

3
T0CR0:139755

4
T0CR0:271646

5
T0CR0:539757

6
T0CR0:311754

And the value is never the same...

Does anybody could help me to find my problem?

  





  

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      Noel Le Moult

    

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    #1183244
  




  

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I have made a mistake in my previous post :

Main code should be :
1
rprintf_devopen(putc_serial0); //Init rprintf

2
rprintf("ADXL2148 Accelerometer Yp raw data :\n\r");

3


4
VICIntEnable |= TIMER0_INT;  //Enable Timer0 Interrupts

5
T0TCR = 0x01;       // TIMER0 Enable 

6


7
while( 1 )

8
{

9
    rprintf("T0CR0:%i\n\r",YPacc);

10
}


And the result output is now :
1
ADXL2148 Accelerometer Yp raw data :

2
T0CR0:4326756

3
T0CR0:4325926

4
T0CR0:4324216

5
T0CR0:4324036

6
T0CR0:4326626

7
T0CR0:4324236


It seems working now.

Thanks

  





  

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      Noel Le Moult

    

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    #1188979
  




  

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I have solved my problem. Here is my personal solution to get the duty 
cycle of the original pwm incoming signal:

Main code :
1
rprintf_devopen(putc_serial0); //Init rprintf

2
rprintf("ADXL2148 Accelerometer Yp raw data :\n\r");

3


4
while( 1 )

5
{

6
    VICIntEnable |= TIMER0_INT; // Enable Timer0 Interrupts

7
    T0TCR = 0x01;               // TIMER0 Enable

8
    delay_ms(20);               // Do some acquisition

9
    T0TCR = 0x00;               // TIMER0 Disable

10
    VICIntEnClr |= TIMER0_INT;  // Stop Timer0 Interrupts

11


12
    result = T1/((T1+T2)/100);  // Duty cycle calculation in percent

13


14
    if( (result > (oldresult+1)) || (result < (oldresult-1)) ) // If detect movement

15
    {

16
        i=100;

17
        rprintf("%d ", result );

18
    }

19


20
}



Interrupt section :
1
static void ISR_Timer0(void)

2
{

3
    //Interrupt Code Here

4
    T0TCR = 0x02;       // TIMER0 Disable; reset T0TC & T0PC

5
    T0PR = 0x00000000;  // Reset T0PR

6


7
    if(state)

8
    {

9
        T1 = T0CR0;

10
        T0CCR = 0x06;   // Capture on CAPn.0 falling edge and Interrupt on CAPn.0 event

11
        state = 0;

12
    }

13
    else

14
    {

15
        T2 = T0CR0;

16
        T0CCR = 0x05;   // Capture on CAPn.0 rising edge and Interrupt on CAPn.0 event

17
        state = 1;

18
    }

19


20
    T0IR = 0xFF;       //Clear the timer interrupt

21
    T0TCR = 0x01;      // TIMER0 Enable

22


23
    VICVectAddr =0;    //Update the VIC priorities

24
}


It should be working, but adjust the "delay_ms(20);" in the main code 
section according to the period of your pwm signal.

  





  

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