A/D Conversion Clock Select bits confussion ..

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  1. - 24th July 2015, 16:06 #1
    HenrikOlsson's Avatar
    HenrikOlsson
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    Default Re: A/D Conversion Clock Select bits confussion ..

    Hi guys,
    OK, doing a dummy conversion on a floating input wasn't the greatest idea....

    I took out the averaging and set up my arb gen to generate 3.3Vpp noise and injected that into AN1 (the dummy channel).

    Code:
    25.6mV input, 10k source resistor, 3.3V noise on "dummy channel":
FOSC/2     2 TAD      Result: 512
FOSC/8     2 TAD      Result: 120
FOSC/32    2 TAD      Result: 23
FRC        2 TAD      Result: 6
FOSC/4     2 TAD      Result: 184
FOSC/16    2 TAD      Result: 54
FOSC/64    2 TAD      Result: 7
FOSC/2     4 TAD      Result: 190
FOSC/8     4 TAD      Result: 59
FOSC/32    4 TAD      Result: 14
FRC        4 TAD      Result: 13
FOSC/4     4 TAD      Result: 117
FOSC/16    4 TAD      Result: 21
FOSC/64    4 TAD      Result: 14
FOSC/2     6 TAD      Result: 127
FOSC/8     6 TAD      Result: 32
FOSC/32    6 TAD      Result: 11
FRC        6 TAD      Result: 11
FOSC/4     6 TAD      Result: 74
FOSC/16    6 TAD      Result: 7
FOSC/64    6 TAD      Result: 10
FOSC/2     8 TAD      Result: 512
FOSC/8     8 TAD      Result: 15
FOSC/32    8 TAD      Result: 15
FRC        8 TAD      Result: 12
FOSC/4     8 TAD      Result: 56
FOSC/16    8 TAD      Result: 10
FOSC/64    8 TAD      Result: 6
FOSC/2     12 TAD     Result: 512
FOSC/8     12 TAD     Result: 11
FOSC/32    12 TAD     Result: 16
FRC        12 TAD     Result: 13
FOSC/4     12 TAD     Result: 31
FOSC/16    12 TAD     Result: 11
FOSC/64    12 TAD     Result: 14
FOSC/2     16 TAD     Result: 512
FOSC/8     16 TAD     Result: 13
FOSC/32    16 TAD     Result: 11
FRC        16 TAD     Result: 11
FOSC/4     16 TAD     Result: 18
FOSC/16    16 TAD     Result: 11
FOSC/64    16 TAD     Result: 9
FOSC/2     20 TAD     Result: 49
FOSC/8     20 TAD     Result: 15
FOSC/32    20 TAD     Result: 10
FRC        20 TAD     Result: 8
FOSC/4     20 TAD     Result: 14
FOSC/16    20 TAD     Result: 10
FOSC/64    20 TAD     Result: 13

***************************************

3.285V, 10k source resistor 3.3V noise on "dummy channel":

FOSC/2     2 TAD      Result: 511
FOSC/8     2 TAD      Result: 861
FOSC/32    2 TAD      Result: 1008
FRC        2 TAD      Result: 1022
FOSC/4     2 TAD      Result: 812
FOSC/16    2 TAD      Result: 963
FOSC/64    2 TAD      Result: 1014
FOSC/2     4 TAD      Result: 511
FOSC/8     4 TAD      Result: 964
FOSC/32    4 TAD      Result: 1021
FRC        4 TAD      Result: 1023
FOSC/4     4 TAD      Result: 888
FOSC/16    4 TAD      Result: 1004
FOSC/64    4 TAD      Result: 1015
FOSC/2     6 TAD      Result: 511
FOSC/8     6 TAD      Result: 994
FOSC/32    6 TAD      Result: 1019
FRC        6 TAD      Result: 1023
FOSC/4     6 TAD      Result: 911
FOSC/16    6 TAD      Result: 1018
FOSC/64    6 TAD      Result: 1019
FOSC/2     8 TAD      Result: 511
FOSC/8     8 TAD      Result: 1006
FOSC/32    8 TAD      Result: 1019
FRC        8 TAD      Result: 1021
FOSC/4     8 TAD      Result: 964
FOSC/16    8 TAD      Result: 1022
FOSC/64    8 TAD      Result: 1016
FOSC/2     12 TAD     Result: 511
FOSC/8     12 TAD     Result: 1015
FOSC/32    12 TAD     Result: 1019
FRC        12 TAD     Result: 1019
FOSC/4     12 TAD     Result: 991
FOSC/16    12 TAD     Result: 1023
FOSC/64    12 TAD     Result: 1015
FOSC/2     16 TAD     Result: 511
FOSC/8     16 TAD     Result: 1014
FOSC/32    16 TAD     Result: 1018
FRC        16 TAD     Result: 1018
FOSC/4     16 TAD     Result: 1005
FOSC/16    16 TAD     Result: 1016
FOSC/64    16 TAD     Result: 1023
FOSC/2     20 TAD     Result: 983
FOSC/8     20 TAD     Result: 1020
FOSC/32    20 TAD     Result: 1017
FRC        20 TAD     Result: 1023
FOSC/4     20 TAD     Result: 1010
FOSC/16    20 TAD     Result: 1017
FOSC/64    20 TAD     Result: 1019
    Then I connected the dummy channel to GND:
    Code:
    25.6mV input, 10k source resistor, "dummy channel" connected to GND:

FOSC/2     2 TAD      Result: 8
FOSC/8     2 TAD      Result: 6
FOSC/32    2 TAD      Result: 8
FRC        2 TAD      Result: 7
FOSC/4     2 TAD      Result: 6
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: 8
FRC        4 TAD      Result: 7
FOSC/4     4 TAD      Result: 6
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: 6
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: 8
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: 8
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: 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: 8
FOSC/16    20 TAD     Result: 8
FOSC/64    20 TAD     Result: 7

*******************************************************

3.285V input, 10k source resistor, "dummy" channel connected to GND:

FOSC/2     2 TAD      Result: 511
FOSC/8     2 TAD      Result: 714
FOSC/32    2 TAD      Result: 996
FRC        2 TAD      Result: 1019
FOSC/4     2 TAD      Result: 610
FOSC/16    2 TAD      Result: 892
FOSC/64    2 TAD      Result: 1018
FOSC/2     4 TAD      Result: 511
FOSC/8     4 TAD      Result: 862
FOSC/32    4 TAD      Result: 1018
FRC        4 TAD      Result: 1018
FOSC/4     4 TAD      Result: 687
FOSC/16    4 TAD      Result: 991
FOSC/64    4 TAD      Result: 1019
FOSC/2     6 TAD      Result: 511
FOSC/8     6 TAD      Result: 955
FOSC/32    6 TAD      Result: 1020
FRC        6 TAD      Result: 1019
FOSC/4     6 TAD      Result: 761
FOSC/16    6 TAD      Result: 1010
FOSC/64    6 TAD      Result: 1019
FOSC/2     8 TAD      Result: 511
FOSC/8     8 TAD      Result: 983
FOSC/32    8 TAD      Result: 1020
FRC        8 TAD      Result: 1018
FOSC/4     8 TAD      Result: 836
FOSC/16    8 TAD      Result: 1018
FOSC/64    8 TAD      Result: 1019
FOSC/2     12 TAD     Result: 511
FOSC/8     12 TAD     Result: 1010
FOSC/32    12 TAD     Result: 1020
FRC        12 TAD     Result: 1019
FOSC/4     12 TAD     Result: 944
FOSC/16    12 TAD     Result: 1019
FOSC/64    12 TAD     Result: 1020
FOSC/2     16 TAD     Result: 511
FOSC/8     16 TAD     Result: 1017
FOSC/32    16 TAD     Result: 1019
FRC        16 TAD     Result: 1018
FOSC/4     16 TAD     Result: 981
FOSC/16    16 TAD     Result: 1020
FOSC/64    16 TAD     Result: 1019
FOSC/2     20 TAD     Result: 511
FOSC/8     20 TAD     Result: 1017
FOSC/32    20 TAD     Result: 1019
FRC        20 TAD     Result: 1019
FOSC/4     20 TAD     Result: 998
FOSC/16    20 TAD     Result: 1021
FOSC/64    20 TAD     Result: 1020
    And finally, dummy channel to Vdd (3.3V):
    Code:
    25.6mV input, 10k source resistor, "dummy channel" connected to Vdd:

FOSC/2     2 TAD      Result: 512
FOSC/8     2 TAD      Result: 344
FOSC/32    2 TAD      Result: 29
FRC        2 TAD      Result: 8
FOSC/4     2 TAD      Result: 432
FOSC/16    2 TAD      Result: 192
FOSC/64    2 TAD      Result: 9
FOSC/2     4 TAD      Result: 512
FOSC/8     4 TAD      Result: 262
FOSC/32    4 TAD      Result: 9
FRC        4 TAD      Result: 8
FOSC/4     4 TAD      Result: 383
FOSC/16    4 TAD      Result: 46
FOSC/64    4 TAD      Result: 8
FOSC/2     6 TAD      Result: 512
FOSC/8     6 TAD      Result: 180
FOSC/32    6 TAD      Result: 8
FRC        6 TAD      Result: 7
FOSC/4     6 TAD      Result: 350
FOSC/16    6 TAD      Result: 17
FOSC/64    6 TAD      Result: 7
FOSC/2     8 TAD      Result: 512
FOSC/8     8 TAD      Result: 99
FOSC/32    8 TAD      Result: 8
FRC        8 TAD      Result: 7
FOSC/4     8 TAD      Result: 312
FOSC/16    8 TAD      Result: 10
FOSC/64    8 TAD      Result: 7
FOSC/2     12 TAD     Result: 512
FOSC/8     12 TAD     Result: 25
FOSC/32    12 TAD     Result: 7
FRC        12 TAD     Result: 8
FOSC/4     12 TAD     Result: 229
FOSC/16    12 TAD     Result: 8
FOSC/64    12 TAD     Result: 7
FOSC/2     16 TAD     Result: 512
FOSC/8     16 TAD     Result: 12
FOSC/32    16 TAD     Result: 7
FRC        16 TAD     Result: 8
FOSC/4     16 TAD     Result: 147
FOSC/16    16 TAD     Result: 7
FOSC/64    16 TAD     Result: 7
FOSC/2     20 TAD     Result: 512
FOSC/8     20 TAD     Result: 9
FOSC/32    20 TAD     Result: 7
FRC        20 TAD     Result: 8
FOSC/4     20 TAD     Result: 66
FOSC/16    20 TAD     Result: 7
FOSC/64    20 TAD     Result: 7

*********************************************


3.285V input, 10k source resistor, "dummy channel" connected to Vdd:

FOSC/2     2 TAD      Result: 1022
FOSC/8     2 TAD      Result: 1021
FOSC/32    2 TAD      Result: 1020
FRC        2 TAD      Result: 1020
FOSC/4     2 TAD      Result: 1022
FOSC/16    2 TAD      Result: 1020
FOSC/64    2 TAD      Result: 1019
FOSC/2     4 TAD      Result: 1022
FOSC/8     4 TAD      Result: 1019
FOSC/32    4 TAD      Result: 1019
FRC        4 TAD      Result: 1019
FOSC/4     4 TAD      Result: 1019
FOSC/16    4 TAD      Result: 1021
FOSC/64    4 TAD      Result: 1020
FOSC/2     6 TAD      Result: 1023
FOSC/8     6 TAD      Result: 1021
FOSC/32    6 TAD      Result: 1019
FRC        6 TAD      Result: 1020
FOSC/4     6 TAD      Result: 1020
FOSC/16    6 TAD      Result: 1020
FOSC/64    6 TAD      Result: 1019
FOSC/2     8 TAD      Result: 1022
FOSC/8     8 TAD      Result: 1020
FOSC/32    8 TAD      Result: 1019
FRC        8 TAD      Result: 1019
FOSC/4     8 TAD      Result: 1020
FOSC/16    8 TAD      Result: 1021
FOSC/64    8 TAD      Result: 1019
FOSC/2     12 TAD     Result: 1022
FOSC/8     12 TAD     Result: 1020
FOSC/32    12 TAD     Result: 1019
FRC        12 TAD     Result: 1020
FOSC/4     12 TAD     Result: 1020
FOSC/16    12 TAD     Result: 1021
FOSC/64    12 TAD     Result: 1020
FOSC/2     16 TAD     Result: 1021
FOSC/8     16 TAD     Result: 1021
FOSC/32    16 TAD     Result: 1019
FRC        16 TAD     Result: 1021
FOSC/4     16 TAD     Result: 1021
FOSC/16    16 TAD     Result: 1019
FOSC/64    16 TAD     Result: 1019
FOSC/2     20 TAD     Result: 1020
FOSC/8     20 TAD     Result: 1021
FOSC/32    20 TAD     Result: 1019
FRC        20 TAD     Result: 1021
FOSC/4     20 TAD     Result: 1018
FOSC/16    20 TAD     Result: 1019
FOSC/64    20 TAD     Result: 1020
    Henrik.
  2. - 25th July 2015, 12:20 #2
    tumbleweed's Avatar
    tumbleweed
    tumbleweed is offline Senior Member
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    Default Re: A/D Conversion Clock Select bits confussion ..

    Thanks Henrik. So again, removing the ones where the ADCS setting is invalid/too fast gives:
    Code:
    25.6mV input, 10k source resistor, 3.3V noise on "dummy channel":

FRC        2 TAD      Result: 6
FOSC/64    2 TAD      Result: 7
FRC        4 TAD      Result: 13
FOSC/64    4 TAD      Result: 14
FRC        6 TAD      Result: 11
FOSC/64    6 TAD      Result: 10
FRC        8 TAD      Result: 12
FOSC/64    8 TAD      Result: 6
FRC        12 TAD     Result: 13
FOSC/64    12 TAD     Result: 14
FRC        16 TAD     Result: 11
FOSC/64    16 TAD     Result: 9
FRC        20 TAD     Result: 8
FOSC/64    20 TAD     Result: 13

*********************************************

3.285V, 10k source resistor 3.3V noise on "dummy channel":

FRC        2 TAD      Result: 1022
FOSC/64    2 TAD      Result: 1014
FRC        4 TAD      Result: 1023
FOSC/64    4 TAD      Result: 1015
FRC        6 TAD      Result: 1023
FOSC/64    6 TAD      Result: 1019
FRC        8 TAD      Result: 1021
FOSC/64    8 TAD      Result: 1016
FRC        12 TAD     Result: 1019
FOSC/64    12 TAD     Result: 1015
FRC        16 TAD     Result: 1018
FOSC/64    16 TAD     Result: 1023
FRC        20 TAD     Result: 1023
FOSC/64    20 TAD     Result: 1019

*********************************************

25.6mV input, 10k source resistor, "dummy channel" connected to GND:

FRC        2 TAD      Result: 7
FOSC/64    2 TAD      Result: 7
FRC        4 TAD      Result: 7
FOSC/64    4 TAD      Result: 7
FRC        6 TAD      Result: 7
FOSC/64    6 TAD      Result: 7
FRC        8 TAD      Result: 7
FOSC/64    8 TAD      Result: 7
FRC        12 TAD     Result: 7
FOSC/64    12 TAD     Result: 7
FRC        16 TAD     Result: 7
FOSC/64    16 TAD     Result: 7
FRC        20 TAD     Result: 7
FOSC/64    20 TAD     Result: 7

*********************************************

3.285V input, 10k source resistor, "dummy" channel connected to GND:

FRC        2 TAD      Result: 1019
FOSC/64    2 TAD      Result: 1018
FRC        4 TAD      Result: 1018
FOSC/64    4 TAD      Result: 1019
FRC        6 TAD      Result: 1019
FOSC/64    6 TAD      Result: 1019
FRC        8 TAD      Result: 1018
FOSC/64    8 TAD      Result: 1019
FRC        12 TAD     Result: 1019
FOSC/64    12 TAD     Result: 1020
FRC        16 TAD     Result: 1018
FOSC/64    16 TAD     Result: 1019
FRC        20 TAD     Result: 1019
FOSC/64    20 TAD     Result: 1020

*********************************************

25.6mV input, 10k source resistor, "dummy channel" connected to Vdd:

FRC        2 TAD      Result: 8
FOSC/64    2 TAD      Result: 9
FRC        4 TAD      Result: 8
FOSC/64    4 TAD      Result: 8
FRC        6 TAD      Result: 7
FOSC/64    6 TAD      Result: 7
FRC        8 TAD      Result: 7
FOSC/64    8 TAD      Result: 7
FRC        12 TAD     Result: 8
FOSC/64    12 TAD     Result: 7
FRC        16 TAD     Result: 8
FOSC/64    16 TAD     Result: 7
FRC        20 TAD     Result: 8
FOSC/64    20 TAD     Result: 7

*********************************************

3.285V input, 10k source resistor, "dummy channel" connected to Vdd:

FRC        2 TAD      Result: 1020
FOSC/64    2 TAD      Result: 1019
FRC        4 TAD      Result: 1019
FOSC/64    4 TAD      Result: 1020
FRC        6 TAD      Result: 1020
FOSC/64    6 TAD      Result: 1019
FRC        8 TAD      Result: 1019
FOSC/64    8 TAD      Result: 1019
FRC        12 TAD     Result: 1020
FOSC/64    12 TAD     Result: 1020
FRC        16 TAD     Result: 1021
FOSC/64    16 TAD     Result: 1019
FRC        20 TAD     Result: 1021
FOSC/64    20 TAD     Result: 1020
    Probably the ones of most interest are where Chold has to swing the full range between samples:
    Code:
    3.285V input, 10k source resistor, "dummy" channel connected to GND:

FRC        2 TAD      Result: 1019
FOSC/64    2 TAD      Result: 1018
FRC        4 TAD      Result: 1018
FOSC/64    4 TAD      Result: 1019
FRC        6 TAD      Result: 1019
FOSC/64    6 TAD      Result: 1019
FRC        8 TAD      Result: 1018
FOSC/64    8 TAD      Result: 1019
FRC        12 TAD     Result: 1019
FOSC/64    12 TAD     Result: 1020
FRC        16 TAD     Result: 1018
FOSC/64    16 TAD     Result: 1019
FRC        20 TAD     Result: 1019
FOSC/64    20 TAD     Result: 1020

*********************************************

25.6mV input, 10k source resistor, "dummy channel" connected to Vdd:

FRC        2 TAD      Result: 8
FOSC/64    2 TAD      Result: 9
FRC        4 TAD      Result: 8
FOSC/64    4 TAD      Result: 8
FRC        6 TAD      Result: 7
FOSC/64    6 TAD      Result: 7
FRC        8 TAD      Result: 7
FOSC/64    8 TAD      Result: 7
FRC        12 TAD     Result: 8
FOSC/64    12 TAD     Result: 7
FRC        16 TAD     Result: 8
FOSC/64    16 TAD     Result: 7
FRC        20 TAD     Result: 8
FOSC/64    20 TAD     Result: 7
    For no averaging those numbers seem pretty reasonable.
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