Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/NXP Semiconductors/LPC11D14/SYSCON/SYSPLLCLKSEL#0x0
SEL=IRC_OSCILLATOR
System PLL clock source select
System PLL clock source
0 (IRC_OSCILLATOR): IRC oscillator
1 (SYSTEM_OSCILLATOR): System oscillator
2 (RESERVED): Reserved
3 (RESERVED): Reserved
Reserved
https://github.com/cmsis-svd/cmsis-svd-data