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Rev. 1.00
42
October 26, 2018
Rev. 1.00
43
October 26, 2018
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
Oscillators
Various oscillator types offer the user a wide range of functions according to their various application
requirements. The flexible 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 configuration options 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 oscillator requiring some external
components and fully integrated internal oscillators requiring no external components, are provided
to form a wide range of both fast and slow system oscillators. 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 flexibility to optimize the
performance/power ratio, a feature especially important in power sensitive portable applications.
Type
Name
Frequency
Pins
Internal High Speed RC
HIRC
8/12/16MHz
—
Internal Low Speed RC
LIRC
32kHz
—
External Low Speed Crystal
LXT
32.768kHz
XT1/XT2
Oscillator Types
System Clock Configurations
There are three methods of generating the system clock, one high speed oscillator and two low speed
oscillators. The high speed oscillator is the internal 8/12/16MHz RC oscillator, HIRC. The two low
speed oscillators are the internal 32kHz RC oscillator, LIRC, and the external 32.768kHz 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. 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.