TAD conversion time per bit

[PROMOD]

TAD=A/D conversion time per bit

Then why is 12TAD required per 10bit conversion? It should have been 10TAD!

[temtronic]

2TAD for discharge... that is shown and explained in the ADC section of the datasheet.Figure 17.4 of the PIC18F46K22, my goto PIC.

For more details as to why,there's a few good apnotes from Microchip, well worth spending an evening to learn how to get the best performance from the ADC section.

Jay

[Ttelmah]

It also does change between chips.
Some of the DsPICs have half cycle steps involved.
Generally the input is disconnected from the capacitor, and one AD clock cycle later the conversion actually starts. Then a bit is generated after each clock, then one more clock is used to latch the final value into the result register.
Some older chips actually add two cycles at the start so 13 cycles rather than 12. Some others have a 2 cycle delay at the end after conversion before starting to reacquire.

[temtronic]

If we assume you're using the 18F4431 then from it's datasheet...

Section 20.9, page 257 ...

After the A/D conversion is completed or aborted, a
2 TAD wait is required before the next acquisition can
be started...

As Mr. T points out different PICS have different specs...ALSO a PIC can have different specs depending on what mode the ADC section has been programmed for. As the designer/programmer, you've got to know how the ADC is to be used and code accordingly.

Also be real careful when laying out the PCB. ANY design over 8 bits and you MUST properly layout the PCB, choose correct parts, power supply and
test for several conditions.

Jay