Using the ADC0808 part seems to be using a ton of I/O pins. 3 for address 1 for address latch, 8 for data, 1 for output enable, 1 for start convert and 1 for end of convert. With the consideration of using three of the bus lines for address output and for data input this total pin complement becomes 12 pins. Personally I would look at a different type of ADC that has a serial interface and can be interfaced to your controller via just a pair of pins. There are many parts of this type available and may give better performance than your ADC0808.

Michael Karas