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XTL2 will not stop

Michael Head
Intellectual 500 points


Hi All,


I am using MSP430F5659IPZ with CCS 5.5.0.00077.  I see about 500 uA current consumption in LPM4.  I have traced this to XTL2 which I can observe oscillating with an oscilloscope.   Just prior to entering LPM4 I have XTL2 pins (Port 7 pins 2, 3 on this device) set as special function to support XTL2.  My UCS registers show no XTL2 use:


SELREF = 010b  (selects REF0CLK)

SELA = 000b  (selects XT1CLK)

SELS = 100b  (selects DCOCLKDIV)

SELM = 100b  (selects DCOCLKDIV)

This MSP430 also has USB which I use.  I see

UPLLEN = 0  (USB PLL disabled)

I see XT2OFF =  1  (disable XT2)


The description of XT2OFF indicates that XT2 is off if not used as a souce for ACLK, MCLK, SMCLK or FLL operation.  I believe that from the registers above I have satisfied this condition.


But my XT2 continues to oscillate, drawing about 500 uA.

I can halt XT2 by setting its port pins back to output

GPIO_setAsOutputPin(GPIO_PORT_P7, GPIO_PIN2);
GPIO_setAsOutputPin(GPIO_PORT_P7, GPIO_PIN3);

In this case XT2 oscillation halts and my 500 uA demand disappears.

Is there some other reason why XT2 oscillation does not stop?  What have I missed?

Thanks!

Mike

  • 0
    Intellectual 500 points
    Oops, guess I've found this problem. XT2OFF was 0 allowing XT2 to be enabled in LPM4. I observed XT2OFF at the wrong time!
  • 0 in reply to Michael Head
    Guru 227245 points
    If a module requests the clock that is sourced by XT2, it won't go off even if XT2OFF is set and LPM4 is entered. Modules can issue unconditional request and conditional requests. You can disable (deny) conditional requests in the PMM.
    Example: If XT2 sources ACLK and ACLK is selected for USCI and USCI is not in reset, then an incoming start byte will re-activate ACLK and therefore XT2, even if the device is in LPM4.

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