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MSC bit on MSP430F2618

steve wenner
Expert 2355 points

I am using an MSP2618 and I am seeing some wierd behavior.  I have a static source that I am putting into an A/D input (360mV).  If I configure the A/D for single conversion (no MSC bit) I see 360mV at the input pin (measured with voltmeter).  If however I set the MSC bit, the minute I step over (in debugger) ADC12CTL0 |= ADC12SC; my voltage goes to 385mV.  I have verified this anomoly on 2 different A/D inputs.  If I disconnect the source and directly measure it, it still reads 360mV.  If I then measure the A/D pin (without source connected), it now reads a voltage of approx. 1.133V.  I have tried all kinds of things like using the PxREN but to no avail.  Any ideas????? 

  • 0
    Guru 227245 points

    steve wenner said:
    the minute I step over (in debugger) ADC12CTL0 |= ADC12SC; my voltage goes to 385mV.

    Oh, yeah! Once more the debugger works as bugger :)
    Never ever use a debugger (especially single-stepping) if you deal with things that are even distantly realtime-related (such as analog signal handling, interface communication etc.)

    The debugger actiosn taken to stop the CPU through JTAG are slow, and invade the CPU heavily. Including stopping clocks etc.
    It's fine for following a program flow or checking algorithms, but when real physical hardware is part of the examination, the debugger may cause more problems than it helps solving.

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