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PGA for MC9S12ZVL

Question asked by Charudatta Ingale on Feb 17, 2016
Latest reply on Feb 18, 2016 by Radek Sestak

Hi all,

Regarding to PGA concept, I have  2 analog signals output from the Low Pass Filter Circuits . These 2 signals are then fed into the microcontroller MC9S12ZVLA as the PGA circuit inputs.

Following are the Register configurations done

PGAEN = 1;

PGAGAIN = 0x02; /* 40x*/

PGAOFFSET = 0x00; /*Disabled OFFSET*/

/* ==== Analog Mode Operation for HVI pin (IGN_FB). ==== */

    PTAL_PTAENL = SET;             /* 1 PL0 is connected to ADC */

    PTAL_PTTEL = SET;             /* Input buffer enabled when used with analog function */

    PTAL_PTADIRL = CLEAR;         /* Input voltage divider active on analog input to ADC channel */

    PIRL_PIRL0 = 0x00;            /* ratio selected 1:6 */

    tPGA settling time given is 56us.

    Vref of ADC is 5v.

When i sample first signal, its is  getting Saturated to 0xFF (Higher than 2.6V) and other Saturated to 0x00 (Negative value less than 2.4V) .

Does anyone know if this could be a problem with the Mux or Settle timing tPGA? do you think we need more time?

 

Also,

I want to know  How long does it take to sample the whole command sequence list to the ADC?

 

Thanks in advance

Charu

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