Hi Mansoon,

The ADC0809 data sheet has a sample schematic of a typical microcontroller interface, using it as memory mapped. The main thing to note is that ALE on the 8051 is not the same as ALE on the 0809.

Is your 8051 connected to external ram/rom? If so you need to take this into account when designing your interface. If you have no external ram/rom you can map the 0809 to low xdata, without needing an address latch, basically just using RD/ and WR/ from P3 as control.

Current limiting resistors on P0? I think you mean pull-up resistors...whether needed or not probably depends on the particular 8051 variant, but most likely yes (P0 has no internal pull-ups on all the 8051s I've worked with).

Personally, I'd rather use the EOC line as an interrupt to let me know when conversion was finished, rather than wasting a timer. The ISR could (should) be as simple as setting a flag that ADC data is available.

If you do use a timer, it will work if your delay is long enough for for conversion to be completed given your ADC clock frequency ("about 100 us" might not be long enough).

Dennis