Prashant

Internal ADC reference selection

Discussion created by Prashant Employee on Sep 23, 2013
Latest reply on Mar 10, 2014 by robin.hu

Q1. The internal ADCs in ADSP-CM40x processors can be configured to select internally generated reference voltage or external reference voltage. How do I select this?

 

A>> By default ADC selects internal 2.5V reference.

It can be turned off and external reference can be selected during Analog Subsystem initialization. While initialising Analog Subsystem, we should program ADCC_CFG.REFSEL bit to select the internal reference or external reference. The Analog subsystem can be initiated by setting ADCC_CTL.ADCFG bit.

 

  1. e.g below code will select external reference.
void Init_AnalogSubsystem(void)
{
 *pREG_ADCC0_TCA0 = (((1 << BITP_ADCC_TCA0_CKDIV ) & BITM_ADCC_TCA0_CKDIV ) |
 ((8 << BITP_ADCC_TCA0_NCK   ) & BITM_ADCC_TCA0_NCK   ) );
 *pREG_ADCC0_TCB0 = (((1 << BITP_ADCC_TCB0_TCSCK ) & BITM_ADCC_TCB0_TCSCK ) | 
 ((0 << BITP_ADCC_TCB0_TCKCS ) & BITM_ADCC_TCB0_TCKCS ) |
 ((11 << BITP_ADCC_TCB0_TCSCS ) & BITM_ADCC_TCB0_TCSCS ) );

    *pREG_ADCC0_TCA1 = (((1 << BITP_ADCC_TCA1_CKDIV ) & BITM_ADCC_TCA1_CKDIV ) |
 ((8 << BITP_ADCC_TCA1_NCK   ) & BITM_ADCC_TCA1_NCK   ) );
 *pREG_ADCC0_TCB1 = (((1 << BITP_ADCC_TCB0_TCSCK ) & BITM_ADCC_TCB0_TCSCK ) | 
 ((0 << BITP_ADCC_TCB0_TCKCS ) & BITM_ADCC_TCB0_TCKCS ) |
 ((11 << BITP_ADCC_TCB0_TCSCS ) & BITM_ADCC_TCB0_TCSCS ) );

 //      Configure ADCC_CFG register
 *pREG_ADCC0_CFG = ((1 << BITP_ADCC_CFG_REFSEL ) & BITM_ADCC_CFG_REFSEL );
 
    // Enable ADCC with 
 // LSBF0, LSBF1, DSWP0, DSWP1, TIDLE0, TIDLE1, CSPOL0, CSPOL1, CKPOL0, CKPOL1 = 0
 // TRGIE0, TRIGIE1 = 0. So, TRGSEL0, TRGSEL1, TRGPOL0, TRGPOL1, TRGOEN0, TRGOEN1 will xx       
 // TMR1EN, DMAEN = 0. CSIZE = 0, DSIZE = 1, CFG = 1;     
 *pREG_ADCC0_CTL   = (BITM_ADCC_CTL_EN | BITM_ADCC_CTL_ADCFG | BITM_ADCC_CTL_DSIZE);
 
 // wait till ADC configuration is pending   
 while(!(*pREG_ADCC0_CFG & BITM_ADCC_CFG_PND)); //    wait for PND bit to set and then wait till it clears
 while(  *pREG_ADCC0_CFG & BITM_ADCC_CFG_PND) ;        //    wait till ADCC operation is pending
 
//      Disable ADCC
 *pREG_ADCC0_CTL = 0x0000; //    disable ADCC first
 while(*pREG_ADCC0_CFG & BITM_ADCC_CFG_PND); //    wait till ADCC operation is pending
}

 

 

When external reference is selected, we have to give external voltage of 2.5V to the VREF0 and VREF1 pins of processor. On ADSP-CM408F EZ-KIT, this can be provided from U6 and U7 ADR441ARMZ chips by installing JP1 and JP4 jumpers.

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