Why not choose an 8051 with a built-in A/D or use an external A/D?

Building your own A/D is likely to take up more PCB space, be more MCU-intensive, could lose dynamic range (i.e. using rail-rail comparator on 5v supply), cost more, and take far longer to design. An A/D has most of the components you need integrated into one chip, plus the manufacturer worried about the myriad details. There is such a wide selection of A/D's that suit most applications and costs.

For my future projects that require A/D and D/A, I am leaning towards using a part with integrated A/D and D/A like most of the Cygnal parts. I figured out that choosing a standard 8051 and throwing on an A/D and D/A costs the same amount as a Cygnal MCU, but in the end the Cygnal PCB is far smaller and the processor is much faster. That sounds like a good change to me!

- Lee