ADC Delays

[demonspells]

on PIC16F877a , 4MHz
how much delay (minimum) should I use after each of those functions:

[temtronic]

I'd suggest 20us between the channel selection and the actual reading. No delay is necessary after reading the ADC.
The datasheet ADC section is full of the real numbers though. Also nothing proves the point better than a real world test. Setup a PIC with say 0,4.99.2.55,0,3.75 precision references on consecutive ADC pins and cut a test program to 'read and display'. After say 10 loops, reduce the delay between channel selection and reading. Sooner or later you'll see what the minimum delay time will be.
Be aware that the 'front end' electronics (stuff before the ADC) will have a bearing on the situation, as well as basic clock speed (4 MHz in your case). Again, that's covered in the datasheets.

[Ttelmah]

No delay is needed after a reading, _but_ a delay is needed before the next reading.
Basically, the internal circuitry is a capacitor, from which the reading is taken. When you perform an ADC conversion, the capacitor is disconnected for the conversion (this gives the sample and hold effect), so there has to be an acquire time to recharge the capacitor _between_ conversions.

Best Wishes

[demonspells]

thank u guys very much
respects
_________________
Badr Ghatasheh

[PCM programmer]