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ADCIN with 18F67K40

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  • ADCIN with 18F67K40


    Section 33.1.2 of the 18F67K40 datasheet contains the following information:

    Important: It is recommended that when switching from an ADC channel of a higher voltage to
    a channel of a lower voltage, the software selects the Vss channel before switching. If the ADC
    does not have a dedicated Vss input channel, the Vss selection (DAC1R<4:0> = b'00000')
    through the DAC output channel can be used. If the DAC is in use, a free input channel can be
    connected to Vss, and can be used in place of the DAC.

    I am assuming ADCIN doesn't "take care" of this situation when using this device. I am not sure how best to meet the requirement. Does it mean that a "dummy" read of Vss must be done between successive ADC conversions?

    Also in this same section is the statement "When changing channels, a delay is required before starting the next conversion." I am a bit confused by this as I can't seem to find a reference as to how long this delay should be.


  • #2
    A "dummy read" would be the only way to do this with ADCIN.

    The define ADC_SAMPLEUS sets the delay time in microseconds. The delay is executed after the channel is set, before the conversion is started.
    Charles Leo
    ME Labs, Inc.


    • #3
      Thanks Charles.