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Problem in TMS320F2808 Related ADC

r n
Prodigy 110 points
Other Parts Discussed in Thread: TMS320F2808

I am using TMS320F2808 in that for ADC if no input is connected  to any channel on evaluation board  it is showing garbage cnt (4095,4096 ) but it is of maximum value. My question is it is like that or problem in my  kit. 

  • 0
    Expert 1710 points

    It has to read something, and maximum value seems as reasonable as any other number with a floating disconnected input pin.  Perhaps someone who looks through the data sheet or who knows the part design thoroughly could see if there's a reason it should have some weak pull up / pull down / virtual ground or whatever tendency that should cause it to settle at a particular value.

    Do make sure that the pins are actually programmed to be ADC inputs and that any other pull up / pull down / I/O functions are disabled for them, of course (I imagine that they're mutually exclusive configurations in one register setting).

    If you're worried about testing the part's ADC function, I would suggest feeding it some kind of ramp waveform input so you can verify that it is really responding to the full set of permitted analog input levels appropriately with the proper resolution / quantization error.  Otherwise your chip inputs could still be "stuck" even if they're just accidentally "stuck" at a common / expected value when floating.