Would the same rules apply for input of ADC of 8052 and cygnal microcontrollers?

Hallo Mahmood,

in most of my projects I used external ADC. Either, because I mostly needed at least 12bit resolution or I needed overvoltage protection scheme provided by some very nice MAXIM ADC.
To combine +-15V analog circuitry with 5V or even 3V digital power supply is not so easy, because either you loose much of input voltage range of ADC or many additional parts for protection circuitry must be added, especially when dealing with multichannel applications.

Once I worked with 80C552, a derivative consisting of 10bit ADC. For this the same rules apply for input of it's ADC. But I made the experience, that so many factors are badly influencing precision of this ADC, that for me this ADC was not very trustworthy...

One major disadvantage was, that ADC of 80C552 needs a slew rate limitation also. Means, analog signal must not change more than one LSB at a certain moment of aquisition timing. But, if so, if there's only a small amount of noise on analog signal in just one critical moment of timing, conversion result is completely out of range! So, it tends to me, that these older micros with internal ADC should not be used for anything else than pure DC signal conversions, in combination with heavy input filtering.

That's my very individual experience with 80C552, but I don't want to talk for others.
May be the time has come to make a next try with micros having an internal ADC...

Kai