Hi,
OK, I did the test.
For this I was using a 18F25K20 running at 64MHz and 3.3V. Vref set to VDD/VSS and measured at 2.999V.
Actual voltages measured with a FLUKE189
The test program cycles thru all the available clock selections and all the available acquisition times (49 combinations). For each selection it takes 8 readings on AN0. Between each reading it makes a dummy conversion of another (floating) channel. After 8 readings it calculates the averages and presents the result.
The test was conducted at 3 different input voltages (25mV, 1.65V, 3.285V) with 3 different source impedences (1k, 10k, 39k). For the 18F25K20 10k is the max recommended source impedence.
Here's the code if anyone wants to repeat the test.
Please note the ADC clock and acquisition time may be different on other devices, this matches the 25K20 that I used:And here are the results:Code:'**************************************************************** '* Name : ADC Test.PBP * '* Author : Henrik Olsson * '* Notice : Copyright (c) 2015 Henrik Olsson * '* : All Rights Reserved * '* Date : 2015-07-23 * '* Version : 1.0 * '* Notes : Test program for verifying ADC clock selection * '* : and acquisition times. * '* : For 18F25K20. * '**************************************************************** DEFINE OSC 64 DEFINE LOADER_USED 1 ' We're using a bootloader. DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1 DEFINE HSER_CLROERR 1 ' Clear overflow automatically DEFINE HSER_SPBRG 138 ' 115200 Baud @ 64MHz, -0,08% SPBRGH = 0 BAUDCON.3 = 1 ' Enable 16 bit baudrate generator ADCON0 = %00000001 ' Enable the ADC, select AN0 ADCON1 = %00000000 ' Vref is Vdd/Vss respectively ADCON2 = %10001000 ' Right justified result, 2TAD, FOosc/2 TRISA.0 = 1 ' RA0/AN0 is input ANSEL.0 = 1 ' Digital buffer disabled, analog enabled Samples VAR BYTE ACQT VAR BYTE ADCS VAR BYTE RESULT VAR WORD Accumulator VAR WORD GODONE VAR ADCON0.1 PAUSE 1000 HSEROUT["Start",10,13] For ACQT = 1 to 7 ' We have 7 different TAD settings ranging from 2TAD to 20TAD For ADCS = 0 to 6 ' We hace 7 different conversion clock selections ADCON2 = 128 + (ACQT * 8) + ADCS ' "Build the ADCON2 word by combining the two settings. PAUSE 25 Accumulator = 0 For samples = 0 to 7 ' Take 8 samples ' First make a dummy conversion of a channel we're not really interested in ADCON0.2 = 1 GODONE = 1 WHILE GODONE : WEND ' Then switch to AN0 and make a conversion. ADCON0.2 = 0 GODONE = 1 WHILE GODONE : WEND ' Get the result and add it to the accumulator Result.HighByte=ADRESH Result.LOWBYTE=ADRESL Accumulator = Accumulator + Result NEXT ' Divide accumulated result by 8 to get the average of our 8 readings. Result = Accumulator >> 3 ' These selections matches the 18F25K20 Select CASE ADCS CASE 0 HSEROUT["FOSC/2 "] CASE 1 HSEROUT["FOSC/8 "] CASE 2 HSEROUT["FOSC/32 "] CASE 3 HSEROUT["FRC "] CASE 4 HSEROUT["FOSC/4 "] CASE 5 HSEROUT["FOSC/16 "] CASE 6 HSEROUT["FOSC/64 "] END Select SELECT CASE ACQT CASE 1 HSEROUT["2 TAD "] CASE 2 HSEROUT["4 TAD "] CASE 3 HSEROUT["6 TAD "] CASE 4 HSEROUT["8 TAD "] CASE 5 HSEROUT["12 TAD "] CASE 6 HSEROUT["16 TAD "] CASE 7 HSEROUT["20 TAD "] END SELECT ' Report the result. HSEROUT[" Result: ", #RESULT, 13] NEXT NEXT PAUSE 100 ENDI haven't analyzed any of it yet and I don't have any more time just now but I wanted to post the results. If anyone wants to graph the results in Excel or whatever to better see what's going on, please feel free to do so.Code:***************************************************** ***************************************************** VRef is VDD/VSS measured to 3.299V 1k resistor in series with input ***************************************************** ***************************************************** Input voltage 25.7mV FOSC/2 2 TAD Result: 8 FOSC/8 2 TAD Result: 8 FOSC/32 2 TAD Result: 7 FRC 2 TAD Result: 7 FOSC/4 2 TAD Result: 8 FOSC/16 2 TAD Result: 7 FOSC/64 2 TAD Result: 7 FOSC/2 4 TAD Result: 9 FOSC/8 4 TAD Result: 7 FOSC/32 4 TAD Result: 7 FRC 4 TAD Result: 7 FOSC/4 4 TAD Result: 8 FOSC/16 4 TAD Result: 7 FOSC/64 4 TAD Result: 7 FOSC/2 6 TAD Result: 8 FOSC/8 6 TAD Result: 7 FOSC/32 6 TAD Result: 7 FRC 6 TAD Result: 7 FOSC/4 6 TAD Result: 7 FOSC/16 6 TAD Result: 7 FOSC/64 6 TAD Result: 7 FOSC/2 8 TAD Result: 8 FOSC/8 8 TAD Result: 7 FOSC/32 8 TAD Result: 6 FRC 8 TAD Result: 7 FOSC/4 8 TAD Result: 7 FOSC/16 8 TAD Result: 7 FOSC/64 8 TAD Result: 7 FOSC/2 12 TAD Result: 8 FOSC/8 12 TAD Result: 8 FOSC/32 12 TAD Result: 7 FRC 12 TAD Result: 7 FOSC/4 12 TAD Result: 7 FOSC/16 12 TAD Result: 7 FOSC/64 12 TAD Result: 7 FOSC/2 16 TAD Result: 8 FOSC/8 16 TAD Result: 7 FOSC/32 16 TAD Result: 7 FRC 16 TAD Result: 7 FOSC/4 16 TAD Result: 7 FOSC/16 16 TAD Result: 7 FOSC/64 16 TAD Result: 7 FOSC/2 20 TAD Result: 8 FOSC/8 20 TAD Result: 7 FOSC/32 20 TAD Result: 7 FRC 20 TAD Result: 7 FOSC/4 20 TAD Result: 7 FOSC/16 20 TAD Result: 7 FOSC/64 20 TAD Result: 7 Input Voltage: 1.650V FOSC/2 2 TAD Result: 497 FOSC/8 2 TAD Result: 509 FOSC/32 2 TAD Result: 511 FRC 2 TAD Result: 511 FOSC/4 2 TAD Result: 508 FOSC/16 2 TAD Result: 511 FOSC/64 2 TAD Result: 511 FOSC/2 4 TAD Result: 504 FOSC/8 4 TAD Result: 511 FOSC/32 4 TAD Result: 511 FRC 4 TAD Result: 511 FOSC/4 4 TAD Result: 512 FOSC/16 4 TAD Result: 511 FOSC/64 4 TAD Result: 511 FOSC/2 6 TAD Result: 507 FOSC/8 6 TAD Result: 511 FOSC/32 6 TAD Result: 511 FRC 6 TAD Result: 511 FOSC/4 6 TAD Result: 512 FOSC/16 6 TAD Result: 511 FOSC/64 6 TAD Result: 511 FOSC/2 8 TAD Result: 509 FOSC/8 8 TAD Result: 511 FOSC/32 8 TAD Result: 511 FRC 8 TAD Result: 511 FOSC/4 8 TAD Result: 512 FOSC/16 8 TAD Result: 511 FOSC/64 8 TAD Result: 511 FOSC/2 12 TAD Result: 511 FOSC/8 12 TAD Result: 511 FOSC/32 12 TAD Result: 511 FRC 12 TAD Result: 512 FOSC/4 12 TAD Result: 512 FOSC/16 12 TAD Result: 511 FOSC/64 12 TAD Result: 511 FOSC/2 16 TAD Result: 511 FOSC/8 16 TAD Result: 511 FOSC/32 16 TAD Result: 511 FRC 16 TAD Result: 511 FOSC/4 16 TAD Result: 512 FOSC/16 16 TAD Result: 511 FOSC/64 16 TAD Result: 511 FOSC/2 20 TAD Result: 511 FOSC/8 20 TAD Result: 511 FOSC/32 20 TAD Result: 511 FRC 20 TAD Result: 511 FOSC/4 20 TAD Result: 512 FOSC/16 20 TAD Result: 512 FOSC/64 20 TAD Result: 511 Input Voltage: 3.286V FOSC/2 2 TAD Result: 511 FOSC/8 2 TAD Result: 1013 FOSC/32 2 TAD Result: 1019 FRC 2 TAD Result: 1019 FOSC/4 2 TAD Result: 995 FOSC/16 2 TAD Result: 1018 FOSC/64 2 TAD Result: 1019 FOSC/2 4 TAD Result: 511 FOSC/8 4 TAD Result: 1019 FOSC/32 4 TAD Result: 1019 FRC 4 TAD Result: 1020 FOSC/4 4 TAD Result: 1011 FOSC/16 4 TAD Result: 1020 FOSC/64 4 TAD Result: 1019 FOSC/2 6 TAD Result: 1006 FOSC/8 6 TAD Result: 1019 FOSC/32 6 TAD Result: 1019 FRC 6 TAD Result: 1020 FOSC/4 6 TAD Result: 1016 FOSC/16 6 TAD Result: 1019 FOSC/64 6 TAD Result: 1019 FOSC/2 8 TAD Result: 1014 FOSC/8 8 TAD Result: 1020 FOSC/32 8 TAD Result: 1019 FRC 8 TAD Result: 1019 FOSC/4 8 TAD Result: 1018 FOSC/16 8 TAD Result: 1019 FOSC/64 8 TAD Result: 1019 FOSC/2 12 TAD Result: 1017 FOSC/8 12 TAD Result: 1019 FOSC/32 12 TAD Result: 1019 FRC 12 TAD Result: 1019 FOSC/4 12 TAD Result: 1020 FOSC/16 12 TAD Result: 1019 FOSC/64 12 TAD Result: 1019 FOSC/2 16 TAD Result: 1019 FOSC/8 16 TAD Result: 1019 FOSC/32 16 TAD Result: 1019 FRC 16 TAD Result: 1019 FOSC/4 16 TAD Result: 1020 FOSC/16 16 TAD Result: 1019 FOSC/64 16 TAD Result: 1019 FOSC/2 20 TAD Result: 1020 FOSC/8 20 TAD Result: 1020 FOSC/32 20 TAD Result: 1019 FRC 20 TAD Result: 1019 FOSC/4 20 TAD Result: 1020 FOSC/16 20 TAD Result: 1020 FOSC/64 20 TAD Result: 1019 ***************************************************** ***************************************************** VRef is VDD/VSS measured to 3.299V 10k resistor in series with input ***************************************************** ***************************************************** Input voltage 25.7mV FOSC/2 2 TAD Result: 9 FOSC/8 2 TAD Result: 8 FOSC/32 2 TAD Result: 7 FRC 2 TAD Result: 7 FOSC/4 2 TAD Result: 8 FOSC/16 2 TAD Result: 7 FOSC/64 2 TAD Result: 7 FOSC/2 4 TAD Result: 8 FOSC/8 4 TAD Result: 7 FOSC/32 4 TAD Result: 7 FRC 4 TAD Result: 7 FOSC/4 4 TAD Result: 8 FOSC/16 4 TAD Result: 7 FOSC/64 4 TAD Result: 7 FOSC/2 6 TAD Result: 8 FOSC/8 6 TAD Result: 7 FOSC/32 6 TAD Result: 7 FRC 6 TAD Result: 7 FOSC/4 6 TAD Result: 7 FOSC/16 6 TAD Result: 7 FOSC/64 6 TAD Result: 7 FOSC/2 8 TAD Result: 8 FOSC/8 8 TAD Result: 7 FOSC/32 8 TAD Result: 7 FRC 8 TAD Result: 7 FOSC/4 8 TAD Result: 7 FOSC/16 8 TAD Result: 7 FOSC/64 8 TAD Result: 7 FOSC/2 12 TAD Result: 8 FOSC/8 12 TAD Result: 7 FOSC/32 12 TAD Result: 7 FRC 12 TAD Result: 7 FOSC/4 12 TAD Result: 7 FOSC/16 12 TAD Result: 7 FOSC/64 12 TAD Result: 7 FOSC/2 16 TAD Result: 8 FOSC/8 16 TAD Result: 8 FOSC/32 16 TAD Result: 7 FRC 16 TAD Result: 7 FOSC/4 16 TAD Result: 8 FOSC/16 16 TAD Result: 7 FOSC/64 16 TAD Result: 7 FOSC/2 20 TAD Result: 8 FOSC/8 20 TAD Result: 7 FOSC/32 20 TAD Result: 7 FRC 20 TAD Result: 7 FOSC/4 20 TAD Result: 7 FOSC/16 20 TAD Result: 7 FOSC/64 20 TAD Result: 7 Input voltage 1.650V FOSC/2 2 TAD Result: 445 FOSC/8 2 TAD Result: 471 FOSC/32 2 TAD Result: 508 FRC 2 TAD Result: 511 FOSC/4 2 TAD Result: 448 FOSC/16 2 TAD Result: 494 FOSC/64 2 TAD Result: 511 FOSC/2 4 TAD Result: 457 FOSC/8 4 TAD Result: 493 FOSC/32 4 TAD Result: 511 FRC 4 TAD Result: 511 FOSC/4 4 TAD Result: 470 FOSC/16 4 TAD Result: 507 FOSC/64 4 TAD Result: 511 FOSC/2 6 TAD Result: 461 FOSC/8 6 TAD Result: 503 FOSC/32 6 TAD Result: 511 FRC 6 TAD Result: 511 FOSC/4 6 TAD Result: 485 FOSC/16 6 TAD Result: 510 FOSC/64 6 TAD Result: 511 FOSC/2 8 TAD Result: 472 FOSC/8 8 TAD Result: 507 FOSC/32 8 TAD Result: 511 FRC 8 TAD Result: 511 FOSC/4 8 TAD Result: 494 FOSC/16 8 TAD Result: 511 FOSC/64 8 TAD Result: 511 FOSC/2 12 TAD Result: 478 FOSC/8 12 TAD Result: 510 FOSC/32 12 TAD Result: 511 FRC 12 TAD Result: 511 FOSC/4 12 TAD Result: 510 FOSC/16 12 TAD Result: 511 FOSC/64 12 TAD Result: 511 FOSC/2 16 TAD Result: 493 FOSC/8 16 TAD Result: 511 FOSC/32 16 TAD Result: 511 FRC 16 TAD Result: 511 FOSC/4 16 TAD Result: 512 FOSC/16 16 TAD Result: 511 FOSC/64 16 TAD Result: 511 FOSC/2 20 TAD Result: 503 FOSC/8 20 TAD Result: 511 FOSC/32 20 TAD Result: 511 FRC 20 TAD Result: 511 FOSC/4 20 TAD Result: 512 FOSC/16 20 TAD Result: 511 FOSC/64 20 TAD Result: 511 Input voltage 3.286V FOSC/2 2 TAD Result: 511 FOSC/8 2 TAD Result: 929 FOSC/32 2 TAD Result: 1012 FRC 2 TAD Result: 1019 FOSC/4 2 TAD Result: 880 FOSC/16 2 TAD Result: 981 FOSC/64 2 TAD Result: 1019 FOSC/2 4 TAD Result: 511 FOSC/8 4 TAD Result: 980 FOSC/32 4 TAD Result: 1018 FRC 4 TAD Result: 1019 FOSC/4 4 TAD Result: 926 FOSC/16 4 TAD Result: 1011 FOSC/64 4 TAD Result: 1019 FOSC/2 6 TAD Result: 511 FOSC/8 6 TAD Result: 1001 FOSC/32 6 TAD Result: 1019 FRC 6 TAD Result: 1020 FOSC/4 6 TAD Result: 959 FOSC/16 6 TAD Result: 1017 FOSC/64 6 TAD Result: 1019 FOSC/2 8 TAD Result: 511 FOSC/8 8 TAD Result: 1010 FOSC/32 8 TAD Result: 1019 FRC 8 TAD Result: 1019 FOSC/4 8 TAD Result: 979 FOSC/16 8 TAD Result: 1019 FOSC/64 8 TAD Result: 1019 FOSC/2 12 TAD Result: 511 FOSC/8 12 TAD Result: 1017 FOSC/32 12 TAD Result: 1020 FRC 12 TAD Result: 1020 FOSC/4 12 TAD Result: 1000 FOSC/16 12 TAD Result: 1019 FOSC/64 12 TAD Result: 1019 FOSC/2 16 TAD Result: 923 FOSC/8 16 TAD Result: 1019 FOSC/32 16 TAD Result: 1019 FRC 16 TAD Result: 1019 FOSC/4 16 TAD Result: 1010 FOSC/16 16 TAD Result: 1019 FOSC/64 16 TAD Result: 1019 FOSC/2 20 TAD Result: 990 FOSC/8 20 TAD Result: 1019 FOSC/32 20 TAD Result: 1019 FRC 20 TAD Result: 1020 FOSC/4 20 TAD Result: 1015 FOSC/16 20 TAD Result: 1019 FOSC/64 20 TAD Result: 1019 ***************************************************** ***************************************************** VRef is VDD/VSS measured to 3.299V 39k resistor in series with input ***************************************************** ***************************************************** Input voltage: 25.7mV FOSC/2 2 TAD Result: 11 FOSC/8 2 TAD Result: 7 FOSC/32 2 TAD Result: 7 FRC 2 TAD Result: 7 FOSC/4 2 TAD Result: 8 FOSC/16 2 TAD Result: 7 FOSC/64 2 TAD Result: 7 FOSC/2 4 TAD Result: 9 FOSC/8 4 TAD Result: 7 FOSC/32 4 TAD Result: 7 FRC 4 TAD Result: 7 FOSC/4 4 TAD Result: 7 FOSC/16 4 TAD Result: 7 FOSC/64 4 TAD Result: 7 FOSC/2 6 TAD Result: 8 FOSC/8 6 TAD Result: 8 FOSC/32 6 TAD Result: 7 FRC 6 TAD Result: 7 FOSC/4 6 TAD Result: 8 FOSC/16 6 TAD Result: 7 FOSC/64 6 TAD Result: 7 FOSC/2 8 TAD Result: 8 FOSC/8 8 TAD Result: 7 FOSC/32 8 TAD Result: 7 FRC 8 TAD Result: 7 FOSC/4 8 TAD Result: 8 FOSC/16 8 TAD Result: 7 FOSC/64 8 TAD Result: 7 FOSC/2 12 TAD Result: 9 FOSC/8 12 TAD Result: 7 FOSC/32 12 TAD Result: 7 FRC 12 TAD Result: 7 FOSC/4 12 TAD Result: 7 FOSC/16 12 TAD Result: 8 FOSC/64 12 TAD Result: 7 FOSC/2 16 TAD Result: 8 FOSC/8 16 TAD Result: 7 FOSC/32 16 TAD Result: 7 FRC 16 TAD Result: 7 FOSC/4 16 TAD Result: 7 FOSC/16 16 TAD Result: 7 FOSC/64 16 TAD Result: 7 FOSC/2 20 TAD Result: 8 FOSC/8 20 TAD Result: 7 FOSC/32 20 TAD Result: 7 FRC 20 TAD Result: 7 FOSC/4 20 TAD Result: 7 FOSC/16 20 TAD Result: 7 FOSC/64 20 TAD Result: 7 Input voltage: 1.650V FOSC/2 2 TAD Result: 406 FOSC/8 2 TAD Result: 420 FOSC/32 2 TAD Result: 470 FRC 2 TAD Result: 507 FOSC/4 2 TAD Result: 407 FOSC/16 2 TAD Result: 441 FOSC/64 2 TAD Result: 496 FOSC/2 4 TAD Result: 408 FOSC/8 4 TAD Result: 439 FOSC/32 4 TAD Result: 495 FRC 4 TAD Result: 511 FOSC/4 4 TAD Result: 418 FOSC/16 4 TAD Result: 469 FOSC/64 4 TAD Result: 509 FOSC/2 6 TAD Result: 415 FOSC/8 6 TAD Result: 457 FOSC/32 6 TAD Result: 505 FRC 6 TAD Result: 511 FOSC/4 6 TAD Result: 428 FOSC/16 6 TAD Result: 485 FOSC/64 6 TAD Result: 511 FOSC/2 8 TAD Result: 418 FOSC/8 8 TAD Result: 469 FOSC/32 8 TAD Result: 509 FRC 8 TAD Result: 512 FOSC/4 8 TAD Result: 442 FOSC/16 8 TAD Result: 495 FOSC/64 8 TAD Result: 511 FOSC/2 12 TAD Result: 427 FOSC/8 12 TAD Result: 486 FOSC/32 12 TAD Result: 511 FRC 12 TAD Result: 511 FOSC/4 12 TAD Result: 456 FOSC/16 12 TAD Result: 506 FOSC/64 12 TAD Result: 511 FOSC/2 16 TAD Result: 450 FOSC/8 16 TAD Result: 496 FOSC/32 16 TAD Result: 511 FRC 16 TAD Result: 512 FOSC/4 16 TAD Result: 469 FOSC/16 16 TAD Result: 509 FOSC/64 16 TAD Result: 511 FOSC/2 20 TAD Result: 453 FOSC/8 20 TAD Result: 502 FOSC/32 20 TAD Result: 511 FRC 20 TAD Result: 511 FOSC/4 20 TAD Result: 478 FOSC/16 20 TAD Result: 510 FOSC/64 20 TAD Result: 511 Input voltage: 3.286V FOSC/2 2 TAD Result: 768 FOSC/8 2 TAD Result: 826 FOSC/32 2 TAD Result: 931 FRC 2 TAD Result: 1010 FOSC/4 2 TAD Result: 801 FOSC/16 2 TAD Result: 873 FOSC/64 2 TAD Result: 986 FOSC/2 4 TAD Result: 511 FOSC/8 4 TAD Result: 867 FOSC/32 4 TAD Result: 984 FRC 4 TAD Result: 1019 FOSC/4 4 TAD Result: 824 FOSC/16 4 TAD Result: 929 FOSC/64 4 TAD Result: 1014 FOSC/2 6 TAD Result: 511 FOSC/8 6 TAD Result: 904 FOSC/32 6 TAD Result: 1006 FRC 6 TAD Result: 1019 FOSC/4 6 TAD Result: 847 FOSC/16 6 TAD Result: 963 FOSC/64 6 TAD Result: 1019 FOSC/2 8 TAD Result: 511 FOSC/8 8 TAD Result: 930 FOSC/32 8 TAD Result: 1014 FRC 8 TAD Result: 1019 FOSC/4 8 TAD Result: 874 FOSC/16 8 TAD Result: 985 FOSC/64 8 TAD Result: 1019 FOSC/2 12 TAD Result: 511 FOSC/8 12 TAD Result: 963 FOSC/32 12 TAD Result: 1019 FRC 12 TAD Result: 1019 FOSC/4 12 TAD Result: 901 FOSC/16 12 TAD Result: 1006 FOSC/64 12 TAD Result: 1019 FOSC/2 16 TAD Result: 847 FOSC/8 16 TAD Result: 985 FOSC/32 16 TAD Result: 1019 FRC 16 TAD Result: 1019 FOSC/4 16 TAD Result: 927 FOSC/16 16 TAD Result: 1015 FOSC/64 16 TAD Result: 1019 FOSC/2 20 TAD Result: 847 FOSC/8 20 TAD Result: 999 FOSC/32 20 TAD Result: 1019 FRC 20 TAD Result: 1019 FOSC/4 20 TAD Result: 950 FOSC/16 20 TAD Result: 1017 FOSC/64 20 TAD Result: 1019
/Henrik.




Bookmarks