Are you REQUIRED to use the 8255 to interface this ADC, or are you simply following a suggestion rather than thinking up a better way?

There are serially interfaced 16-bit ADC's, such as a few from WWW.MAXIM-IC.COM that don't require a 16-bit interface. You probably should have a look at them before making a selection. The effort and cost to produce 16-bit resolution will easily outweigh the cost of a microcontroller that either contains the ADC, or at least supports a convenient serial interface such as those from MAXIM and other vendors. If you carefully implement your circuit EXACTLY as recommended by the manufacturer, and with a minimum of components, you might, if you're lucky, get 12-bit or better precision. 16 bit resolution is easy, as other have said, but attaining 16-bit accuracy, particuarly with a 16-bit converter, takes great skill and effort. It also will REQUIRE a very precise voltage reference, and, of course, a power supply with much less noise than the one part in 65536 that 16 bit resolution requires. It will require very precise passive components, not just the typical 5%-20% types found in the lab at University.

RE