Conversion of an analog input selected by the multiplexer occurs in this block. It contains a digital-to-analog capacitor (DAC) array, a comparator and a successive approximation register. Each conversion is a sequence of eight comparisons operations, beginning with the MSB. Each comparison determines the value of a bit in the successive approximation register(SAR). The DAC array performs two functions. It acts as a sample and hold circuit during the entire conversion sequence, and provides comparison voltage to the comparator during each successive comparison.
The result of each successive comparison is stored in the SAR, and when the conversion sequence is complete, the contents of the SAR are transferred to the appropriate result register.