INTRODUCTION

When using the internal Analog to Digital Converter of the ST62 family and maximum A/D converter accuracy is required, it is desirable to filter out any noise present on the analog input, but also noise present on the ground and VCC supply lines of the MCU as VCC is also the voltage reference of the A/D converter. Good decoupling must be made with capacitors on the analog input and between VCC and ground. It is also recommended to put the MCU in wait state while the conversion is in progress, so as to minimize noise injected into VCC by the operation of the micro-controller itself.

Finally, when enough time is available, it is highly recommended to make several successive A/D conversions and take an average of the results. This is the most effective way to get the most accuracy out of the ST6 family A/D converter.

The following code fragment demonstrates a burst of 256 successive measurements, after which the average is put into the accumulator. The whole routine takes approximately 30 milli seconds with an 8 MHz clock. When less time is available, it is of course possible to reduce the number of conversions: 8, 16 or 32 conversions also give good results, although the most con versions give the best results.