MSP43O - Strange Behaviour in LPM's after modifing SELS bit

[electro]

Hi,

I use MSP430F148 or MSP430F149.

Circuit connections are as follows:

DVCC, AVCC are connected to 3V
DVSS, AVSS, VeREF+ (pin10), VREF- (pin11) are connected to GND
RST/NMI pin is tied to VCC over 100K resistor.
Only JTAG interface pins are connected to 14-pin JTAG-Connector
All other pins are floating. (I/O, XT1, XT2, Vref+)

F148 datasheet says LPM3 consumes approximately 2uA at 3V.

When i try this in my code (IAR KickStart):

// --- Start of Code
#include <msp430x14x.h>
#include "defs.h"

void main(void)
{
WDTCTL = WDTPW + WDTHOLD; // WATCHDOG TIMER OFF

LPM3; // Enter LPM3 (SCG1=1,SCG0=1,OSCOFF=0,CPUOFF=1)
}
// --- End of Code

Current consumption is 2uA at 3V. So everything is OK.



Now, consider this lines of code:

// --- Start of Code
#include <msp430x14x.h>
#include "defs.h"

void main(void)
{
WDTCTL = WDTPW + WDTHOLD; // WATCHDOG TIMER OFF

// Initial value of BCSCTL2 is 0x00,
// Know set and than reset SELS bit, so return to initial state
BCSCTL2=0x08; // Set SELS bit, Use XT2CLK for generating SMCLK
BCSCTL2=0x00; // Reset SELS bit, Use DCOCLK for generating SMCLK

LPM3; // Enter LPM3 (SCG1=1,SCG0=1,OSCOFF=0,CPUOFF=1)
}
// --- End of Code

This time current consumption increases to approximately 250uA at 3V.

There is a huge difference in current ratings between these 2 codes.
I do not understand why this happens.
I have tried many ways but can not get rid of this problem. (Other LPM modes caused the same problem)
Please, try running these codes on your MSP430. You will notice the strange current raise.


Any comments/ideas are welcome.

Best regards
Alper YILDIRIM