Datasheet

MCLK_request
CPUOFF
SCG1
SELS
SMCLK_request
SELM0
XSELM1
XT2OFF
XT2off (Internal Signal)
XT2 is an Internal Signal
XT2 = 0: Devices without XT2 oscillator
XT2 = 1: Devices with XT2 oscillator
ACLK_request
MCLK_request
OSCOFF
CPUOFF
SCG1
SELS
SMCLK_request
SELM0
XSELM1
XT2
XTS
LFOff
XT1Off
LFXT1Off
www.ti.com Basic Clock Module+ Operation
Figure 5-3. Off Signals for the LFXT1 Oscillator
NOTE: LFXT1 Oscillator Characteristics
Low-frequency crystals often require hundreds of milliseconds to start up, depending on the
crystal.
Ultralow-power oscillators such as the LFXT1 in LF mode should be guarded from noise
coupling from other sources. The crystal should be placed as close as possible to the
MSP430 with the crystal housing grounded and the crystal traces guarded with ground
traces.
5.2.4 XT2 Oscillator
Some devices have a second crystal oscillator, XT2. XT2 sources XT2CLK and its characteristics are
identical to LFXT1 in HF mode. The XT2Sx bits select the range of operation of XT2. The XT2OFF bit
disables the XT2 oscillator if XT2CLK is not used for MCLK or SMCLK as shown in Figure 5-4.
XT2 may be used with external clock signals on the XT2IN pin when XT2Sx = 11 and XT2OFF = 0. When
used with an external signal, the external frequency must meet the data sheet parameters for XT2. When
the input frequency is below the specified lower limit, the XT2OF bit may be set to prevent the CPU from
being clocked with XT2CLK.
Figure 5-4. Off Signals for Oscillator XT2
5.2.5 Digitally-Controlled Oscillator (DCO)
The DCO is an integrated digitally controlled oscillator. The DCO frequency can be adjusted by software
using the DCOx, MODx, and RSELx bits.
5.2.5.1 Disabling the DCO
Software can disable DCOCLK by setting SCG0 when it is not used to source SMCLK or MCLK in active
mode, as shown in Figure 5-5.
277
SLAU144J–December 2004–Revised July 2013 Basic Clock Module+
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