Explain the pin diagram of ADC 0808/0809 and method of interfacing to 8086 microprocessor with a suitable example.
  • ADC 0809 is an 8 channel, 8 bit ADC. It can convert an analog voltage input into an 8 bit digital data output.
  • To select an input out of 8 options, there are three select lines (C, B and A). We put a channel number on these lines (0…7) and latch it using ALE. SOC signal is given to indicate start of conversion.
  • The channel voltage is internally sampled and held into a capacitor. Conversion takes place internally using “Successive Approximations Algorithm”.
  • Reference voltage for conversion is provided using +Vref and –Vref. The clock supply needed for conversion is given through CLK (typically ~ 1MHz).
  • The end of conversion is indicated by the ADC using EOC signal. Now we give the OE signal enabling 8-bit data output from the ADC to 8255.
  • This data from 8255 is now transferred to the microprocessor. The process is repeated for subsequent channels, by changing the channel number. ADCs have a vast use in the modern electronic world for Data Acquisition Systems. They can be used for temperature sensing, voice recording, speed sensing etc.
  • Interfacing of ADC 0809 with 8086 using 8255 is represented in figure below:

Interfacing of ADC 0809 and 8086 using 8255

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