33.5 Computation Operation

The ADC module hardware is equipped with post conversion computation features. These features provide data post-processing functions that can be operated on the ADC conversion result, including digital filtering/averaging and threshold comparison functions.

Figure 33-11. Computational Features Simplified Block Diagram
The operation of the ADC computational features is controlled by the ADMD bits.

The module can be operated in one of five modes:

  • Basic: This is a legacy mode. In this mode, ADC conversion occurs on single (ADDSEN = 0) or double (ADDSEN = 1) samples. ADIF is set after each conversion is complete.
  • Accumulate: With each trigger, the ADC conversion result is added to the accumulator and ADCNT increments. ADIF is set after each conversion. ADTIF is set according to the calculation mode.
  • Average: With each trigger, the ADC conversion result is added to the accumulator. When the ADRPT number of samples have been accumulated, a threshold test is performed. Upon the next trigger, the accumulator is cleared. For the subsequent tests, additional ADRPT samples are required to be accumulated.
  • Burst Average: At the trigger, the accumulator is cleared. The ADC conversion results are then collected repetitively until ADRPT samples are accumulated and finally the threshold is tested.
  • Low-Pass Filter (LPF): With each trigger, the ADC conversion result is sent through a filter. When ADRPT samples have occurred, a threshold test is performed. Every trigger after that the ADC conversion result is sent through the filter and another threshold test is performed.

The five modes are summarized in the following table.

Table 33-4. Computation Modes
Register Clear Event Value after Cycle(2) Completion Threshold Operations Value at ADTIF Interrupt
Mode ADMD ADACC and ADCNT ADACC(1) ADCNT Retrigger Threshold Test Interrupt ADAOV ADFLTR ADCNT
Basic 0 ADACLR = 1 Unchanged Unchanged No Every Sample If threshold=true N/A N/A count
Accumulate 1 ADACLR = 1 S1 + ADACC

or

(S2-S1) + ADACC

 If (ADCNT=FF): ADCNT, otherwise: ADCNT+1 No Every Sample If threshold=true ADACC Overflow ADACC/2ADCRS count
Average 2 ADACLR = 1 or ADCNT>=ADRPT at ADGO or retrigger S1 + ADACC

or

(S2-S1) + ADACC

 If (ADCNT=FF): ADCNT, otherwise: ADCNT+1 No If ADCNT>=ADRPT If threshold=true ADACC Overflow ADACC/2ADCRS count
Burst

Average

 3 ADACLR = 1 or ADGO set or retrigger Each repetition: same as Average

End with sum of all

samples

 Each repetition: same as Average

End with ADCNT=ADRPT

 Repeat while ADCNT<ADRPT If ADCNT>=ADRPT If threshold=true ADACC Overflow ADACC/2ADCRS ADRPT
Low-pass Filter 4 ADACLR = 1 S1+ADACC-ADACC/
2ADCRS

or

(S2-S1)+ADACC-ADACC/2ADCRS

 If (ADCNT=FF): ADCNT, otherwise: ADCNT+1 No If ADCNT>=ADRPT If threshold=true ADACC Overflow Filtered Value count
Note:
  1. S1 and S2 are abbreviations for Sample 1 and Sample 2, respectively. When ADDSEN = 0, S1 = ADRES; When ADDSEN = 1, S1 = ADPREV and S2 = ADRES.
  2. When ADDSEN = 0 then Cycle means one conversion. When ADDSEN = 1 then Cycle means two conversions.