SPRUIZ1B July 2023 – August 2024 TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1
Configuring different ADCs to use different resolutions results in asynchronous operation. This occurs because the conversion time for 12-bit mode and 16-bit mode are different. Synchronous operation requires both the start and end of the conversion phase to be aligned, so even using the same S+H window duration does not result in synchronous operation.
Example: Asynchronous Operation with Different Resolutions
//ADCA = 12-bit mode
AdcaRegs.ADCSOC0CTL.bit.CHSEL = 4; //SOC0 converts ADCINA4
AdcaRegs.ADCSOC0CTL.bit.ACQPS = 50; //SOC0 uses sample duration of 51 SYSCLK cycles
AdcaRegs.ADCSOC0CTL.bit.TRIGSEL = 10; //SOC0 begins conversion on ePWM3 SOCB
//ADCB = 16-bit mode
AdcbRegs.ADCSOC0CTL.bit.CHSEL = 0; //SOC0 converts ADCINB0/B1
AdcbRegs.ADCSOC0CTL.bit.ACQPS = 50; //SOC0 uses sample duration of 51 SYSCLK cycles
AdcbRegs.ADCSOC0CTL.bit.TRIGSEL = 10; //SOC0 begins conversion on ePWM3 SOCB
To achieve synchronous operation while using both 12-bit and 16-bit resolution, conversions must be done in parallel at one resolution. Once conversions are complete at one resolution, the CPU must switch the resolution on all ADCs and then cause another trigger (this trigger must not be a software SOC force, as all ADCs cannot be started simultaneously using this method).