HT46R064D/065D/066D
Enhanced A/D Type 8-Bit OTP MCU with LED Driver
External 32768Hz Crystal Oscillator - LXT
When the microcontroller enters the Sleep Mode, the system clock is switched off to stop
microcontroller activity and to conserve power. However, in many microcontroller applications it may
be necessary to keep the internal timers operational even when the microcontroller is in the
Power-down Mode. To do this, another clock, independent of the system clock, must be provided. To
do this a configuration option exists to allow a high speed oscillator to be used in conjunction with a a
low speed oscillator, known as the LXT oscillator. The LXT oscillator is implemented using a
32768Hz crystal connected to pins OSC1/OSC2 for the HT46R064D/HT46R065D/HT46R066D.
However, for some crystals, to ensure oscillation and accurate frequency generation, it is necessary to
add two small value external capacitors, C1 and C2. The exact values of C1 and C2 should be selected
in consultation with the crystal or resonator manufacturer¢s specification. The external parallel
feedback resistor, Rp, is required. For the HT46R064D/HT46R065D/HT46R066D devices the LXT
oscillator must be used together with the HIRC oscillator.
External LXT Oscillator - LXT
LXT Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
32768Hz
8pF
10pF
Note: 1. C1 and C2 values are for guidance only.
2. RP=5M~10MW is recommended.
32768 Hz 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 CTRL0 register.
LXTLP Bit
LXT Mode
Quick Start
Low-power
0
1
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 re-
duced current consumption, as the higher current consumption is only required during the LXT oscil-
lator 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.
Rev. 1.00
29
January 12, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
