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Rev. 1.20
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Rev. 1.20
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HT69F30A/HT69F40A/HT69F50A
TinyPower
TM
I/O Flash 8-Bit MCU with LCD & EEPROM
HT69F30A/HT69F40A/HT69F50A
TinyPower
TM
I/O Flash 8-Bit MCU with LCD & EEPROM
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 Bit
LXT Mode
0
Qui�k Sta�t
1
Low-powe�
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 one of the low frequency oscillator choices, which is
selected via configuration option. 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%.
External Clock – EC
The system clock can also be supplied by an externally supplied clock giving users a method of
synchronizing their external hardware to the microcontroller operation. This is selected using
a configuration option and supplying the clock on pin OSC1. Pin OSC2 should be left floating
if the external oscillator is used. The internal oscillator circuit contains a filter circuit to reduce
the possibility of erratic operation due to noise on the oscillator pin, however as the filter circuit
consumes a certain amount of power, a oscillator configuration option exists to turn this filter off.
Not using the internal filter should be considered in power sensitive applications and where the
externally supplied clock is of a high integrity and supplied by a low impedance source.
Supplementary Oscillators
The low speed oscillators, in addition to providing a system clock source are also used to provide a
clock source to two other device functions. These are the Watchdog Timer, the LCD driver and the
Time Base Interrupts.