Texas Instruments MSP430x1xx - Manual (Page 104)

LFXT1 and XT2 Oscillators
7-4
7.2 LFXT1 and XT2 Oscillators
The Basic Clock Module includes the LFXT1 oscillator and, in some configura-
tions, a second XT2 oscillator.
7.2.1 LFXT1 Oscillator
The LFXT1 oscillator starts operating on a valid PUC condition. A valid PUC
condition resets the OscOff bit in the status register, which enables LFXT1.
Software can disable LFXT1 by setting OscOff, if this signal does not source
SMCLK or MCLK.
The design of the LFXT1 oscillator (shown in Figure 7–2) supports the
low-current consumption feature and the use of a 32,768-Hz watch crystal
when in LF mode (XTS=0). A watch crystal connects to the clock module via
two terminals without any other external components. Components necessary
to stabilize the clock operation have been integrated into the MSP430.
The design of the LFXT1 oscillator also supports high-speed crystals or
resonators when in HF mode (XTS = 1). The crystal or resonator connects to
the terminals and requires external capacitors on both terminals. These
capacitors should be sized according to crystal or resonator specifications.
Figure 7–2. Principle of LFXT1 Oscillator
XT1Off
Oscillator
Fault Detect LFOff
OscOff XTS
1 0
1 0
XIN
XOUT
LFXT1_OscFault
LFXT1CLK
Low Power
LF Oscillator, XTS = 0
The OscOff bit in the status register is used to turn off LFXT1CLK if this signal
does not source MCLK or SMCLK.