The accuracy of the A/D Converter is indicated by an absolute accuracy. The absolute accuracy refers to a difference expressed by LSB between the output code obtained by A/D converting the analog input voltages and the output code expected for an A/D converter with ideal characteristics. The analog input voltages used during accuracy measurement are the midpoint values of the voltage width in which an A/D converter with ideal characteristics produces the same output code. If Vref = 5.12 V, for example, the width of 1 LSB for a 10-bit A/D converter is 5 mV, so that 0 mV, 5 mV, 10 mV, 15 mV, 20 mV, 25 mV and so on are selected as midpoints of the analog input voltage. If an A/D converter is said to have the absolute accuracy of ±2 LSB, it means that if the input voltage is 25 mV, for example, the output code expected for an A/D converter with ideal characteristics is 005h, and the actual A/D conversion result is in the range of 003h to 007h. Note that the absolute accuracy includes zero, fullscale, differential non-linearity (DNL), integral nonlinearity (INL), and quantization errors. When actually using the A/D Converter, the analog input voltages are in the range of 0V to Vref. Note, however, that low Vref voltages result in a poor resolution. Note also that output codes for the analog input voltages from Vref to AVcc are always 3FFh.