HT45R22E Holtek Semiconductor, HT45R22E Datasheet - Page 23

• Manufacturer Part Number: HT45R22E
• Description: Remote Type 8-bit OTP MCU
• Manufacturer: Holtek Semiconductor

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. How-
ever, 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 appli-
cation 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 func-
tion normally. The only difference is that it will take more
time to start up if in the Low-power mode.
Internal Low Speed Oscillator - LIRC
The LIRC is a fully self-contained free running on-chip
RC oscillator with a typical frequency of 10kHz at 3V re-
quiring no external components. When the device en-
ters 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.
Operating Modes
By using the LXT low frequency oscillator in combina-
tion with a high frequency oscillator, the system can be
selected to operate in a number of different modes.
These Modes are Normal, Slow, Idle and Sleep.
Rev. 1.00
LXTLP Bit
0
1
Quick Start
LXT Mode
Low-power
System Clock Configurations
23
Mode Types and Selection
The higher frequency oscillators provide higher perfor-
mance but carry with it the disadvantage of higher
power requirements, while the opposite is of course true
for the lower frequency oscillators. With the capability of
dynamically switching between fast and slow oscillators,
the device has the flexibility to optimise the perfor-
mance/power ratio, a feature especially important in
power sensitive portable applications.
If the LXT oscillator is used, then the internal RC oscilla-
tor, HIRC, must be used as the high frequency oscillator.
If the HXT or the ERC oscillator is chosen as the high
frequency system clock, then the LXT oscillator cannot
be used for sharing the same pins. The CLKMOD bit in
the CTRL0 register can be used to switch the system
clock from the high speed HIRC oscillator to the low
speed LXT oscillator. When the HALT instruction is exe-
cuted and the device enters the Idle/Sleep Mode, the
LXT oscillator will always continue to run. For this device
the LXT crystal is connected to the OSC1/OSC2 pins
and LXT will always run (the LXT oscillator enable con-
trol bit is not used). Note that CLKMOD is only valid in
HIRC+LXT oscillator configuration.
Operating
Normal
Slow
Sleep
Mode
HXT
Stop
Run
Operating Mode Control
OSC1/OSC2 Configuration
ERC
Stop
Run
HIRC
Stop
Run
HT45R22E
HIRC
March 17, 2010
Stop
Stop
Run
HIRC + LXT
unimplemented
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LXT
Run
Run
Run