BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 30

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

BS2824/BS2854/BS2868
Touch Key MCU
Rev. 1.00
LXT Oscillator Low Power Function
Internal Low Speed Oscillator - LIRC
For the BS2868, a configuration option determines if the XT1/XT2 pins are used for the LXT oscilla-
tor or as I/O pins.
The LXT oscillator can function in one of two modes, the Quick Start Mode and the Low Power
Mode. The mode selection is executed using the LXTLP bit in the CTRL0 register.
After power on the LXTLP bit will be automatically cleared to zero ensuring that the LXT oscillator
is in the Quick Start operating mode. In the Quick Start Mode the LXT oscillator will power up and
stabilise quickly. However, after the LXT oscillator has fully powered up it can be placed into the
Low-power mode by setting the LXTLP bit high. The oscillator will continue to run but with
reduced current consumption, as the higher current consumption is only required during the LXT
oscillator start-up. In power sensitive applications, such as battery applications, where power
consumption must be kept to a minimum, it is therefore recommended that the application program
sets the LXTLP bit high about 2 seconds after power-on.
It should be noted that, no matter what condition the LXTLP bit is set to, the LXT oscillator will
always function normally, the only difference is that it will take more time to start up if in the
Low-power mode.
The LIRC is a fully self-contained free running on-chip RC oscillator with a typical frequency of
13kHz at 5V requiring no external components. When the device enters the Idle/Sleep Mode, the
system clock will stop running but the WDT oscillator continues to free-run and to keep the
watchdog active. However, to preserve power in certain applications the LIRC can be disabled via a
configuration option.
If the I/O option is selected then the XT1/XT2 pins can be used as normal I/O pins.
If the LXT oscillator is selected then the 32kHz crystal should be connected to the XT1/ XT2
pins.
LXTLP Bit
0
1
30
Quick Start
Low-power
LXT Mode
January 27, 2010