SPRUJF2A March 2026 – March 2026 AM13E23019
The XTAL takes time to start after being enabled. A startup monitor is provided to indicate to the application software if the XTAL has successfully started, at which point the HFCLK can be selected to source a variety of system functions. The HFCLK startup monitor also supports checking the HFCLK_IN digital clock input for a clock stuck fault.
To enable the HFCLK startup monitor, clear the HFCLKFLTCHK bit in the HFCLKCLKCFG register in SYSCTL (the default state is disabled).
When XTAL is started or the HFCLK_IN is selected as the HFCLK source, the HFCLKGOOD and HFCLKOFF bits in the CLKSTATUS register in SYSCTL are cleared.
In the case of XTAL being used, after the specified XTAL startup time has expired the XTAL status is tested. If the XTAL started successfully, the XTAL startup monitor asserts the HFCLKGOOD bit in the CLKSTATUS register and the HFCLKGOOD interrupt is also asserted. If the XTAL did not start within the specified startup time, the HFCLKOFF bit is set, indicating that the XTAL was dead at startup.
In the case of HFCLK_IN being used, after HFCLK_IN is selected a clock stuck check is performed. If the clock is alive, the HFCLKGOOD bit is set in the CLKSTATUS register and the HFCLKGOOD interrupt is also asserted. If the HFCLK_IN signal was stuck, the HFCLKOFF bit in CLKSTATUS register is set, indicating that the HFCLK_IN is dead.
If desired, checking of the HFCLK by the HFCLK startup monitor can be left disabled by keeping the HFCLKFLTCHK bit set in the HFCLKCLKCFG register in SYSCTL.