what is exact Tacq necessory and how to use PIC18F2550

[ep.hobbyiest]

I am using pic18f2550 pic. and configuring ADC. but in that i am not geting exactly acquasition time require for ADC. Is time we have to wait for ADC conversion or start up time.?
Is that delay for conversion?
i m using pic at 20MHz crystal.

- - - Updated - - -

TACQ = Amplifier Settling Time + Holding Capacitor Charging Time + Temperature Coefficient
= TAMP + TC + TCOFF

In this formula what is to take TAMP?
is it fixed of 0.2 us or depends on Machine cycle time.?
and other parameters are fixed i think.

 

[esp1]

hi,
The d/s for the 18F2550 shows the Tamp [ Amp settling time as typically 0.2uS.]

Use the values and formula shown in Fig #21-3.

This gives the time period you must wait before reading the ADC registers.

E

 

[ep.hobbyiest]

Thanks but i saw that page.
This what formula i have written but i didn't get the concept plz explain.

 

[esp1]

hi ep.
I see that some of the values used in the d/s formula example are incorrect.?:?:

I will check further and let you know what I find.

Eric

 

[esp1]

hi ep,
Checking the maths and stated values in the 18F2550 datasheet for the AD acquisition times shows that the example is wrong.
Perhaps other members could double check my conclusions.? [shown in the attached image]

I have compared a number of d/s for the 16F and 18F and it appears that 'older' parts of the 16F series d/s ADC data has been copied into the 18F series d/s.

Look thru this adc.pdf for guidance on how to calculate the Tacq and the conversion times for the ADC.
Page #18 shows the use of the ADCONO.GO flag usage to check that the conversion is complete.

E