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athornsb

Unusual Power Draw - Launchpad

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The ADC shouldn't be running if it's not doing a conversion.  Its ADC10OSC turns on/off as needed (assuming that is what you've selected for it).  I was just reading the MSP430 x2xx User's Guide on this last week, it's meant to facilitate very-low-power applications.

 

Ok so that means I dont need to set ADC10 Data Transfer Control or ADC10 Control bits?  Again thanks, I've programmed a Renesas micro controller before, but never a TI, so a lot of this is new to me. 

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The guy from the launchpad workshop video mentioned setting all unused pins as output, then using the internal pullup/down to either set a pullup/down on those unused pins as well. Is this effectlivly the same thing ? I do notice that grace pretty much does exactly what you say here though too.

Not sure, the datasheet doesn't mention that explicitly (just to enable the pulldown resistor but doesn't explicitly mention setting PxOUT or PxDIR).

 

I'd think since the schmitt trigger hardware is enabled regardless of the PxDIR setting (assuming I'm looking at the datasheet's pin schematics correctly), it'd make the most sense to set PxDIR = 0 to avoid draining/sourcing large amounts of current in case you short one of the unused pins to a voltage reference... and enable the pulldown (or pullup, both should be OK) resistor to clamp the pin to a known state.  Shorting the pin to GND or Vcc would still draw current with input mode + pullup/down resistor, just a lot less (only whatever the pullup/down resistor can give).

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Ok so that means I dont need to set ADC10 Data Transfer Control or ADC10 Control bits?  Again thanks, I've programmed a Renesas micro controller before, but never a TI, so a lot of this is new to me. 

RX series by chance?  I noticed there was a book for that RX62N authored by a professor at UNC Charlotte :)  I have that board, been trying to figure it out a piece at a time myself...

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Oh just to give you a little more info about the project..... It's incredibly simple.

We need an MSP430 connected to a solar cell or cells, a 3 digit LCD, and a graycode switch.  The MCU will let users change a single parameter with the switch, and output the value to the display.  It also must run off a relatively small solar cell, and spend much of its time in a low light space.  We are designing a little additional hardware to power it (cap(s) and maybe a charge pump, so instantaneous power draw isnt much of a concern).

 

I don't anticipate needing more than 2 counter interrupts and a single switch interrupt, so we really just want the thing asleep in LPM3 as much as possible.  

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RX series by chance?  I noticed there was a book for that RX62N authored by a professor at UNC Charlotte :smile:  I have that board, been trying to figure it out a piece at a time myself...

 

Actually it's a senior project.  We are using a G series launchpad for now, but will be transitioning to a 1 series chip on a bread board once all of the code works.

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Actually it's a senior project.  We are using a G series launchpad for now, but will be transitioning to a 1 series chip on a bread board once all of the code works.

Ah, was asking about the Renesas chips :)

 

For the ADC, the main bit I'm talking about is this excerpt from page 551 of the x2xx User's Guide (slau144i)-

 

22.2.4 Auto Power-Down

The ADC10 is designed for low power applications.  When the ADC10 is not actively converting, the core is automatically disabled and is automatically re-enabled when needed.  The ADC10OSC is also automatically enabled when needed and disabled when not needed.  When the core or oscillator is disabled, it consumes no current.

 

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Ah, was asking about the Renesas chips :smile:

 

For the ADC, the main bit I'm talking about is this excerpt from page 551 of the x2xx User's Guide (slau144i)-

That's perfect, thanks.  I'm gonna head off and watch the low power video for anything I missed, and then go back to the lab and re test this thing!

 

Oh and it may have been, I can't remember (I assumed this was some TI chip i wasn't familiar with).  I used it in a class for NC State, but that class is actually moving away from Renesas in favor of TI now.

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The guy from the launchpad workshop video mentioned setting all unused pins as output, then using the internal pullup/down to either set a pullup/down on those unused pins as well. Is this effectlivly the same thing ? I do notice that grace pretty much does exactly what you say here though too.

This is a tiny detail I ran into with another project:

Setting POUT high and PREN low drives the output high.

Setting POUT high and PREN high sets the output in pull up mode.

While PREN is high, PDIR does not affect the output! However, is PDIR is low, the pin input circuitry is still enabled, which might draw a microscopic amount of power. IF PDIR is high the PIN is linked tighter to the core to POUT (so pulling the pin low externally wil not affect PIN anymore).

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