Oscillators; Oscillato� Ove�View; System Clock Configurations - Holtek BS83B24C Manual

BS83B24C/BS83C40C
Touch Flash MCU

Oscillators

Various oscillator options 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 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 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 the registers. 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 have the flexibility to optimize the performance/power ratio, a feature
especially important in power sensitive portable applications.
Inte�nal High Speed RC
Inte�nal Low Speed RC
Exte�nal Low Speed C��stal

System Clock Configurations

There are three methods of generating the system clock, a high speed oscillator and two low speed
oscillators. The high speed oscillator is the internal 8/12/16MHz RC oscillator, HIRC. The low
speed oscillator is the external 32.768kHz crystal oscillator, LXT, and the internal 32kHz RC
oscillator, LIRC. 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 registers. 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.
Rev. 1.00
Type Name
HIRC
LIRC
LXT
Oscillator Types
43
Freq. Pins
�/1�/16MHz —
3�kHz —
3�.�6�kHz XT1/XT�
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