Set
Reset
Q
Set
Reset
Q
Set
Q
Q
Set
Reset
PUC
NMI _ IRQA
OFIFG
OFIE
NMIRS
Set
Reset
Q
Set
Reset
Q
LFXTOFFG
HFXTOFFG
LFXT_OF
HFXT_OF
POR
HFXT_OscFault
OscFault_Clr
OscFault_Set
Q
Q
LFXT_OscFault
Clock System Operation
101
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Clock System (CS) Module
Figure 3-3. Oscillator Fault Logic
NOTE:
Fault conditions
LFXT_OscFault:
When the fault detection logic is enabled (ENLFXTD = 1), this signal is set
after the LFXT oscillator has stopped operation and is cleared after operation resumes. The
fault condition causes LFXTOFFG to be set and remain set. If the user clears LFXTOFFG
and the fault condition still exists, LFXTOFFG remains set.
HFXT_OscFault:
When the fault detection logic is enabled (ENHFXTD = 1), this signal is set
after the HFXT oscillator has stopped operation and is cleared after operation resumes. The
fault condition causes HFXTOFFG to be set and remain set. If the user clears HFXTOFFG
and the fault condition still exists, HFXTOFFG remains set.
NOTE:
Fault logic
As long as a fault condition still exists, the OFIFG remains set. The application must take
special care when clearing the OFIFG signal. If no fault condition remains when the OFIFG
signal is cleared, the clock logic switches back to the original user settings before the fault
condition.
NOTE:
The LFXT startup includes a counter that ensures that 1024 valid clock cycles have passed
before LFXT_OscFault signal is cleared. A valid cycle is any cycle that meets the frequency
requirement (f
Fault,LF
) as outlined in the device specific data sheet. Any crystal fault restarts the
counter. It is recommended that the counter always be enabled, however the counter can be
disabled by clearing ENSTFCNT1.
Similarly, HFXT startup also includes a counter that ensures that 1024 valid clock cycles
have passed before HFXT_OscFault signal is cleared. This counter can be disabled by
clearing ENSTFCNT2.
The disabling of the counters is valid for bypass and normal modes of operation.