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Rev. 1.21
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HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
External LXT Oscillator
LXT Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
32.�68kHz
1�pF
1�pF
�ote: 1. C1 and C2 values a�e fo� guidance only.
2. R
P
=5MΩ~10MΩ is recommended.
32.768kHz Crystal Recommended Capacitor Values
LXT Oscillator Low Power Function
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 TBC register.
LXTLP
LXT Mode
�
Quick Sta�t Mode
1
Low Powe� Mode
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.
Internal 32kHz Oscillator – LIRC
The Internal 32kHz System Oscillator is the low frequency oscillator. It is a fully integrated
RC oscillator with a typical frequency of 32kHz at 5V, requiring no external components for its
implementation. Device trimming during the manufacturing process and the inclusion of internal
frequency compensation circuits are used to ensure that the influence of the power supply voltage,
temperature and process variations on the oscillation frequency are minimised. As a result, at a
power supply of 5V and at a temperature of 25
°C
degrees, the fixed oscillation frequency of 32kHz
will have a tolerance within 10%.
Supplementary Oscillator
The low speed oscillator, in addition to providing a system clock source is also used to provide
a clock source to two other device functions. These are the Watchdog Timer and the Time Base
Interrupts.