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MSP430F2274-EP: Current draw increases significantly when using P2.6 as a GPIO in LPM4

adevries
Intellectual 945 points
Part Number: MSP430F2274-EP
Other Parts Discussed in Thread: MSP430F2274

Hello,

I have an MSP430F2274 I am putting in LPM4. When I initially did this, I measured the current draw in LPM4 to be <0.7uA. Next, I wanted to use P2.6 as a general purpose input and wake up on a signal transition interrupt. So, I set P2SEL to 0x80 and enabled the interrupt, and now when I am in LPM4, the current draw is more than 7uA! The only difference between these two measurements is the clearing BIT6 of P2SEL to use it as an input. The electrical connection to pin P2.6 remain the same. I have pin P2.6 externally pulled up to VCC with a 100k resistor, and another device's open-drain output connecting to the circuit. 

Does anyone know why changing P2.6 from XIN to a general purpose input would cause such a large change in current? This isn't the case for other GPIO pins I'm using as inputs...

Thanks

  • 0
    Guru 100785 points

    P2.6 and P2.7 operate in tandem. Generally, if you want to use P2.6 as GPIO, you should clear the P2SEL for P2.7 as well. There are hints in the books, but this is mostly observed behavior:

    https://e2e.ti.com/support/microcontrollers/msp430/f/166/p/850446/3151256

  • 0 in reply to Bruce McKenney
    Intellectual 945 points

    Hi Bruce,

    Thanks for the response. I didn't mention it in my original post, but I initially tried clearing P2SEL for both P2.7 and P2.6. Rather than helping, that seemed to make the problem worse, with the total LPM consumption being about 10uA. I found the best band-aid was to set P2SEL to 0x40. For whatever reason, the majority of the excess current seems to happen when BIT 6 of P2SEL is cleared. Have you seen this behavior happen before on other MSP430's XIN/XOUT pin?

  • 0 in reply to adevries
    Guru 100785 points

    I haven't experimented with it much. On the (few) F2 designs I did without a crystal, I avoided them.

    Some other suggestions:

    1) Did you make sure the LFXT is switched off by setting LFXT1S=2 (VLO)? That was discussed over in the other thread, but the effects were inconclusive. I did once see it clear up the effects (repeated failovers) of a bad solder joint in my crystal circuit.

    2) Once you have the pins as GPIO, you need to muzzle them (if not connected) or the Schmitt trigger will "jiggle" and draw power. I usually use input-pulldown, but some prefer output-high.

  • 0 in reply to Bruce McKenney
    Intellectual 945 points

    Hi Bruce,

    Thanks for the further ideas. I actually figured out what the issue was today. Long story short, P2.6 was actually floating. I thought I had it pulled up high, but I was wrong. Setting P2.6 as a GPIO input and pulling it high solved my issue. Thank you for all the help!

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