Content originally posted in LPCWare by R2D2 on Sat Mar 07 06:56:13 MST 2015
User Manual 10398:
Quote:
3.4 Clock generation
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The LPC111x/LPC11Cxx include[color=#f00] three independent oscillators. These are the system oscillator, the Internal RC oscillator (IRC), and the watchdog oscillator[/color]. Each oscillator can be used for more than one purpose as required in a particular application.
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Following reset, the LPC111x/LPC11Cxx will operate from the Internal RC oscillator until switched by software. This allows systems to operate without any external crystal and the bootloader code to operate at a known frequency
Datasheet:
Quote:
When the system oscillator is not used, connect XTALIN and XTALOUT as follows: XTALIN can be left floating or can be grounded (grounding is preferred to reduce susceptibility to noise). XTALOUT should be left floating.
So system oscillator is whatever you connect to XTALIN / XTALOUT: usually a (12MHz) crystal :O