Rev. 1.60 66 August 20, 2019 Rev. 1.60 67 August 20, 2019
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
Oscillators
Various oscillator types offer the user a wide range of functions according to their various application
requirements. The exible features of the oscillator functions ensure that the best optimisation can
be achieved in terms of speed and power saving. Oscillator selections and operation are selected
through a combination of application program and relevant control registers.
Oscillator Overview
In addition to being the source of the main system clock the oscillators also provide clock sources
for the Watchdog Timer and Time Base Interrupts. External oscillators requiring some external
components as well as fully integrated internal oscillators, requiring no external components, are
provided to form a wide range of both fast and slow system oscillators. All oscillator options are
selected through register programming. The higher frequency oscillators provide higher performance
but carry with it the disadvantage of higher power requirements, while the opposite is of course true
for the lower frequency oscillators. With the capability of dynamically switching between fast and
slow system clock, the device has the exibility to optimize the performance/power ratio, a feature
especially important in power sensitive portable applications.
Type Name Frequency Pins
External High Speed Crystal HXT 400 kHz~20 MHz OSC1/OSC2
Internal High Speed RC HIRC 8/12/16 MHz —
External Low Speed Crystal LXT 32.768 kHz XT1/XT2
Internal Low Speed RC LIRC 32 kHz —
Oscillator Types
System Clock Congurations
There are four methods of generating the system clock, two high speed oscillators for all devices and
two low speed oscillators. The high speed oscillator is the external crystal/ceramic oscillator, HXT,
and the internal 8/12/16 MHz RC oscillator, HIRC. The two low speed oscillators are the internal 32
kHz RC oscillator, LIRC, and the external 32.768 kHz crystal oscillator, LXT. Selecting whether the
low or high speed oscillator is used as the system oscillator is implemented using the CKS2~CKS0
bits in the SCC register and as the system clock can be dynamically selected.
The actual source clock used for the low speed oscillators is chosen via the FSS bit in the SCC
register while for the high speed oscillator the source clock is selected by the FHS bit in the SCC
register. The frequency of the slow speed or high speed system clock is determined using the
CKS2~CKS0 bits in the SCC register. Note that two oscillator selections must be made namely one
high speed and one low speed system oscillators. It is not possible to choose a no-oscillator selection
for either the high or low speed oscillator.
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