Understanding Vref

The voltage applied to the reference input, Vref, defines the voltage span of the analog input, over which the 256 possible output values apply. When Vref = V+ = +5V, the A/D converter's maximum voltage is set to +5V. The minimum value is 0V or ground.

Therefore the voltage spans 5V over a range of 256 possible values. Each of the 256 possible values, or levels, thus represents:

5 V / 256 levels = 0.0195 volts per level which, for practical purposes, we will round off to 0.02 volts.

For example, if the A/D converter returned a reading of 52, the voltage represented is: 52 * 0.02 = 1.04 V Your Turn

Calculate the voltages represented by the following A/D converter readings:

87 10 221 100

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