BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 27

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

Oscillator
Rev. 1.00
Wake-up Function Register - PAWK
Pull-high Registers - PAPU, PBPU, PCPU, PDPU, PFPU
Software COM Register - SCOMC
System Oscillator Overview
System Clock Configurations
When the microcontroller enters the Idle/Sleep Mode, various methods exist to wake the device up
and continue with normal operation. One method is to allow a falling edge on the I/O pins to have a
wake-up function. This register is used to select which Port A I/O pins are used to have this wake-up
function.
The I/O pins, if configured as inputs, can have internal pull-high resistors connected, which eliminates
the need for external pull-high resistors. This register selects which I/O pins are connected to internal
pull-high resistors.
The pins PB0~PB3 on Port B can be used as SCOM lines to drive an external LCD panel. To
implement this function, the SCOMC register is used to setup the correct bias voltages on these pins.
Various oscillator options offer the user a wide range of functions according to their various
application requirements. The flexible features of the oscillator functions
optimisation can be achieved in terms of speed and power saving. Oscillator selections and operation are selected
through a combination of configuration options and registers.
In addition to being the source of the main system clock the oscillators also provide clock sources for
the Watchdog Timer and Time Base functions. External oscillators requiring some external
components as well as a two fully integrated internal oscillators, requiring no external components,
are provided to form a wide range of both fast and slow system oscillators.
There are five system oscillators. Three high speed oscillators and two low speed oscillators. The
high speed oscillators are the external crystal/ceramic oscillator - HXT, the external - ERC, and the
internal RC oscillator - HIRC. The two low speed oscillator are the external 32768Hz oscillator -
LXT and the internal 13kHz (V
* BS2868 only
External Crystal
External RC
Internal High Speed RC
External Low Speed Crystal
Internal Low Speed RC
Type
DD
Name
HIRC
LIRC
=5V) oscillator - LIRC.
ERC
HXT
LXT
27
BS2824/BS2854/BS2868
400kHz~12MHz
400kHz~12MHz
4, 8 or 12MHz
32768Hz
13kHz
Freq.
Touch Key MCU
OSC1/OSC2
OSC1/OSC2
XT1/XT2*
OSC1
Pins
ensure that the best
January 27, 2010