Difference between ADC channels

Discussion in 'General Electronics Chat' started by R!f@@, Apr 22, 2014.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    While I was going thru the pics I have regarding this situation I came across something that confuses me.

    In 12F683 the data says 10-bit A/D(ch) is 4 in the table

    • A/D converter:
    - 10-bit resolution and 4 channels

    In 16F88 the data says 10-bit A/D(ch) is 1 in the table

    • 10-bit, 7-channel A/D converter
    Now I can count the AN pins on both PIC
    12F683 has 4 ch.
    16F88 has 7 ch.

    What I do not get is the 4 & 1 part.
    Why did the 16F88 says 1 instead of 7.

    Aren't all the AN channels in PIC's multiplexed ?

    Or is it a typo ?

    One other thing is the block diagram on 16F88 does not show separate Analog inputs and it's A2D converter block while the 12F683 does.

    Does the Vref has anything to do with it ?

    Some one care to explain this part to dumb ol' me . :D

    Sorry for not attaching the pdf's. I am at home and it's annoyingly slow connection time. :mad: with a fast connection as they claim
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    There is 1 ADC module, which is multiplexed with X input pins. You can only ADC on 1 input pin at a time.

    Some of the higher spec PICs have more than 1 ADC module.

    From memory all the 16F PICs have either zero ADC modules or just 1 ADC module.

    Regarding the datasheets, they are written over different years and they change the way they say things, as years progress. You just have to stumble through it and check all the diagrams etc, as you correctly did. :)
     
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  3. R!f@@

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    So, 12F683 and 16F88 has 1 ADC module each.
     
  4. ericgibbs

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    Jan 29, 2010
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    hi R!,
    The 12F683 has 4 channels, ie : 4 active ADC pins.
    E
     
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  5. t06afre

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    May 11, 2009
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    Yes and they use an analog mux to route signals into the ADC. This is concept is also quite common in most multi channel ADC ICs
     
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  6. R!f@@

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    Apr 2, 2009
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    Yup ! I know F638 has 4 and F88 has 7 ADC ch


    I was looking at the diagram. F683 shows a block labeled ADC, and F88 does not.
    It just confused me, tht's why I needed to know more about that area.

    F683 shows a Vref at ADC block but F88 shows no Vref.
    Does it mean F683 Vref can be assigned values other than Vdd.

    Before we discussed Vref in other thread and I came to believe that F88 Vref cannot be changed and it is fixed at Vdd
     
  7. R!f@@

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    Active ADC's ?

    Aren't the ADC's activated during coding.

    I do not get the part "Active"
     
  8. t06afre

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    On general basis most PIC micros with ADC. Will allow you to alocate one specific analog input pin as ADC reference or use VDD as reference. If you look in the datasheet at FIGURE 12-1: A/D BLOCK DIAGRAM (http://ww1.microchip.com/downloads/en/DeviceDoc/30487D.pdf) You will see that you can select two reference voltages. VREF+ and VREF- It is common to use GND as VREF- and then use either VDD or the AN3 for external reference
     
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