Texas Instruments MSP430x1xx - Manual (Page 106)

LFXT1 and XT2 Oscillators
7-6
7.2.3 Oscillator Fault Detection
An analog circuit controls the operation of oscillators LFXT1 and XT2 and flags
an oscillator fault when approximately 100 cycles (at 1 MHz) of the crystal are
missed. The active OSCFault signal sets the oscillator-fault-interrupt flag
(OFIFG) and requests a non-maskable interrupt when the oscillator-fault inter-
rupt enable bit (OFIE) is set. User software must clear the OFIFG flag.
Figure 7–5. Oscillator-Fault-Interrupt
XT_OscFault
S
Clear
NMIFG
NMIRS
OFIFG
OFIE
PUC IRQA
IE1.1
IFG1.1
XT1off
LFXT1_OscFault
POR
XT2off
XT2_OscFault
XT2
Oscillator Fault NMI
Fault_from
XT2
Fault_from
XT1
XTS
SELM.1
SELM.0
DCOR
Select DCO including Internal Resistor XT Oscillator Fails
XT2 Is an internal signal
XT2 = 0: Two oscillators – MSP430x11x and MSP430x11x1 devices
XT2 = 1: Three oscillators – MSP430F13x and MSP430F14x devices
IRQA: Interrupt request accepted
XSELM.1
XDCOR
The XT2_OscFault signal of the XT2 oscillator, and the LFXT1_OscFault sig-
nal of the LFXT1 oscillator will set the oscillator-fault-interrupt flag (OFIFG) in-
dependently
. During two-oscillator implementation, the oscillator-fault-inter-
rupt flag can be reset by software if the LFXT1_OscFault signal is a logic low.
During three-oscillator implementation, the oscillator-fault-interrupt flag can
be reset by software only if both oscillator-fault signals, LFXT1_OscFault and
XT2_OscFault, are low.