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.
- 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.
