MSP430F149 Sampling Rate

Hi,

I want to find out the dynamic parameters of the ADC12 embedded in the
MSP430F149.

I want to know how I can maximize my sample rate.  So far, I was only
able to run it at 128 ksps, but the datasheet said I could run it at
200 ksps.  If anyone could help me with this matter, I'd really
appreciate it.  Thank you.

- Amy

> I want to find out the dynamic parameters of the ADC12 embedded in the
> MSP430F149.
>
> I want to know how I can maximize my sample rate.  So far, I was only
> able to run it at 128 ksps, but the datasheet said I could run it at
> 200 ksps.  If anyone could help me with this matter, I'd really
> appreciate it.  Thank you.

We do this successfully.  I think you'll need your MSP430 running at full 
MCLK but you can test if it's possible to make the target sample rate at a 
lower MCLK.

Here's my setup code:

void adcInitFast(void)
{
 #define MIN_TIMERB ((SMCLK / 200000) - 1)
 UINT16 timerB;
 int i;

 // TIMERB source is SMCLK, count up to TBCCR0
 TBCTL = TBSSEL_2 | MC_1;

 // TIMERB OUT0 is PULSE
 TBCCTL0 = OUTMOD_3;

 // TIMERB OUT1 is square wave
 TBCCTL1 = OUTMOD_3;

 // Select the ADC input pin for ADC12
 P6SEL |= BIT0;
 P6DIR &= ~BIT0;

 // Disable conversion to allow changes to the ADC12
 ADC12CTL0 = 0;

 // Configure ADC: Conversion start address 0, TIMERB.OUT0 is sample input 
signal, MCLK drives ADC12, repeat single channel
 ADC12CTL1 = CSTARTADD_0 | SHS_2 | SHP | ADC12DIV_0 | ADC12SSEL_2 | 
CONSEQ_2;

 // No ADC12 interrupts
 ADC12IE = 0;

 // Configure TIMERA: SMCLK steps timer, divide by 8, halted, clear
 TACTL = TASSEL1 | ID1 | ID0 | TACLR;

 // Compute the timer terminal value
 timerB = (word)(((float)(SMCLK) / gProbeTable.pyroSampleRate) + 0.5F) - 1;

 // Limit the sample clock to the maximum ADC12 sample rate
 if(timerB < MIN_TIMERB) timerB = MIN_TIMERB;

#ifdef MAXIMUM_SAMPLE_RATE
 timerB = 4;
#endif

 // Load the sample clock terminal value
 TBCCR0 = timerB;

 // Disable conversion to allow changes to the ADC12
 ADC12CTL0 = 0;

 // Select the reference voltage
 ADC12MCTL0 = SREF_1;

 // Turn on ADC12
 ADC12CTL0 = REF2_5V | REFON | ADC12ON | SHT0_1;

 // Delay for reference start-up
 for(i = 0; i < 500; i++);

 // Enable conversion
  ADC12CTL0 |= ENC;

 // This starts the sampling
 i = (int)(ADC12MEM0);
 while(!(ADC12IFG & BIT0));
}

Here's how I read the ADC at 200KHz:

 UINT16 adc;

 for(;;)
 {
  // Get the next sample
  while(!(ADC12IFG & BIT0));
  adc = ADC12MEM0;
 }

Keep in mind these important considerations:

1. You won't be able to service interrupts and sustain 200KHz continuous 
sample rate.
2. You won't be able to service ADC interrupts (IOW, you need to poll).
3. There's not a lot of processing time after you read the ADC result.
4. YMMV

JJS

> I want to find out the dynamic parameters of the ADC12 embedded in the
> MSP430F149.
>
> I want to know how I can maximize my sample rate.  So far, I was only
> able to run it at 128 ksps, but the datasheet said I could run it at
> 200 ksps.  If anyone could help me with this matter, I'd really
> appreciate it.  Thank you.

We do this successfully.  I think you'll need your MSP430 running at full
MCLK but you can test if it's possible to make the target sample rate at a
lower MCLK.

Here's my setup code:

void adcInitFast(void)
{
 #define MIN_TIMERB ((SMCLK / 200000) - 1)
 UINT16 timerB;
 int i;

 // TIMERB source is SMCLK, count up to TBCCR0
 TBCTL = TBSSEL_2 | MC_1;

 // TIMERB OUT0 is PULSE
 TBCCTL0 = OUTMOD_3;

 // TIMERB OUT1 is square wave
 TBCCTL1 = OUTMOD_3;

 // Select the ADC input pin for ADC12
 P6SEL |= BIT0;
 P6DIR &= ~BIT0;

 // Disable conversion to allow changes to the ADC12
 ADC12CTL0 = 0;

 // Configure ADC: Conversion start address 0, TIMERB.OUT0 is sample input
signal, MCLK drives ADC12, repeat single channel
 ADC12CTL1 = CSTARTADD_0 | SHS_2 | SHP | ADC12DIV_0 | ADC12SSEL_2 |
CONSEQ_2;

 // No ADC12 interrupts
 ADC12IE = 0;

 // Configure TIMERA: SMCLK steps timer, divide by 8, halted, clear
 TACTL = TASSEL1 | ID1 | ID0 | TACLR;

 // Compute the timer terminal value
 timerB = (word)(((float)(SMCLK) / gProbeTable.pyroSampleRate) + 0.5F) - 1;

 // Limit the sample clock to the maximum ADC12 sample rate
 if(timerB < MIN_TIMERB) timerB = MIN_TIMERB;

#ifdef MAXIMUM_SAMPLE_RATE
 timerB = 4;
#endif

 // Load the sample clock terminal value
 TBCCR0 = timerB;

 // Disable conversion to allow changes to the ADC12
 ADC12CTL0 = 0;

 // Select the reference voltage
 ADC12MCTL0 = SREF_1;

 // Turn on ADC12
 ADC12CTL0 = REF2_5V | REFON | ADC12ON | SHT0_1;

 // Delay for reference start-up
 for(i = 0; i < 500; i++);

 // Enable conversion
  ADC12CTL0 |= ENC;

 // This starts the sampling
 i = (int)(ADC12MEM0);
 while(!(ADC12IFG & BIT0));
}

Here's how I read the ADC at 200KHz:

 UINT16 adc;

 for(;;)
 {
  // Get the next sample
  while(!(ADC12IFG & BIT0));
  adc = ADC12MEM0;
 }

Keep in mind these important considerations:

1. You won't be able to service interrupts and sustain 200KHz continuous
sample rate.
2. You won't be able to service ADC interrupts (IOW, you need to poll).
3. There's not a lot of processing time after you read the ADC result.
4. YMMV

JJS

Hi John,

Thank you for your reply.  We tried the polling, and it works! Thanks
a lot :)

- Amy