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MSP430F1611: Calculating sample time for extended mode

Messay Tamire
Prodigy 30 points
Part Number: MSP430F1611

I wanted to calculate the sample time for extended mode. as written in the manual in the extended mode the SAMPCON will stay high for SHI high time (basically controlled by this signal). what I am not understanding is what SHI signal is? it says that SHI source can be selected using SHSx bits which is from ADC12SC bit, TImer_A Output Unit 1 , The Timer_B Output Unit 0, and Timer_B Output Unit1. does this mean if I choose SHS bit to be Timer_A Ouput Unit1 my SHI signal is identical to this?

and also what is the ADC12SC bit doing there how could it be a source.

  • 0
    Guru 88510 points

    The notion behind User Guide (SLAU049F) Figs 17-3/4: For a timer trigger (SHS>0), SHI comes from the timer output (OUTMOD), effectively a PWM pulse. You don't need to route the output to a pin -- setting SHS is enough. SAMPCON is an internal signal generated based on SHI, SHP and SHT.

    With SHP=0, the sample/hold time is as long as the High portion of the SHI pulse. With SHP=1, the sample/hold period is started by the leading edge of the pulse, and is as long as specified in the SHT field (the trailing edge doesn't matter). 

    I'm pretty sure that with SHS=0 and SHP=0 you use the SC bit (high then low) to create this PWM pulse. (I think I did this by accident once.) This combination isn't very useful since the sample/hold period depends on the CPU instruction timing so it's difficult to determine how long it actually is.

    [Edit: Minor re-wording]

  • 0 in reply to Bruce McKenney47378
    Prodigy 30 points

    Okay, I understand now. Thank you.

  • 0 in reply to Bruce McKenney47378
    Prodigy 30 points

    May I also ask, when SHS=0 ADC12SC bit is 1, and for this, we need to route the output pin? assuming we set SHP=1 and setting SHT or just the bit 1 is important to trigger the sampling session.

  • 0 in reply to Messay Tamire
    Guru 88510 points

    As far as I know there isn't an external pin for ADC12SC, so no, you don't need to route a pin for this case either. With SHP=1 (and SHS=0), you set SC=1 and it clears by itself.

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