A good question to ask here is, “How fast can the D/A be driven?” According to the Nyquist criteria, output samples have to be taken at a rate at least 2x the highest frequency in the signal the user wishes to re-create. For the H8S/2148A MCU, the fastest conversion time is 10µs, which equates to a 100kHz sample rate. In theory, then, this performance would allow them to recreate up to a 50kHz waveform. However, there are two main problems with generating a signal of the maximum frequency. Delivering data accurately at 10µs intervals is the major problem. Processor performance is the issue. Typically, the maximum output frequency created will be limited to less than 10kHz so that users will have sufficient processing power available for the other tasks their embedded system must perform. The other problem deals with the requirements for the filter. If a sample is taken at only twice the frequency of the signal that is being recreated, the D/A’s output waveform will impose difficult requirements on the filter design. Specifically, the filter will have to have a very sharp cutoff in order to eliminate ripple from the output signal. If instead samples are taken at a higher rate (and thus limit the maximum frequency of the output signal that is generated) then a simpler, less expensive low-pass filter can be used.