HT48R02N Holtek Semiconductor, HT48R02N Datasheet - Page 22

• Manufacturer Part Number: HT48R02N
• Description: (HT4xR0xx) Small Package 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

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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 and Sleep.
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 Sleep Mode the LXT os-
cillator will always continue to run. For the device the
LXT crystal is connected to the OSC1/OSC2 pins and
LXT will always run.
Note that CLKMOD is only valid in HIRC+LXT oscillator
configuration.
When the system enters the Sleep Mode, the high fre-
quency system clock will always stop running. The ac-
companying tables shows the relationship between the
CLKMOD bit, the HALT instruction and the high/low fre-
quency oscillators. The CLMOD bit can change normal
or Slow Mode.
Rev.1.00
System Clock Configurations
22
Mode Switching
The devices are switched between one mode and an-
other using a combination of the CLKMOD bit in the
CTRL0 register and the HALT instruction. The CLKMOD
bit chooses whether the system runs in either the Nor-
mal or Slow Mode by selecting the system clock to be
sourced from either a high or low frequency oscillator.
The HALT instruction forces the system into either the
Sleep Mode, depending upon whether the LXT oscilla-
tor is running or not. The HALT instruction operates in-
dependently of the CLKMOD bit condition.
When a HALT instruction is executed and the LXT oscil-
lator is not running, the system enters the Sleep mode
the following conditions exist:
Operating
Normal
Slow
Sleep
The system oscillator will stop running and the appli-
cation program will stop at the HALT instruction.
The Data Memory contents and registers will maintain
their present condition.
The WDT will be cleared and resume counting if the
WDT clock source is selected to come from the WDT
or LXT oscillator. The WDT will stop if its clock source
originates from the system clock.
Mode
Operating Mode Control
HXT
Stop
Run
HT46R01B/02B/01N/02N
HT48R01B/02B/01N/02N
OSC1/OSC2 Configuration
ERC
Stop
Run
HIRC
Stop
Run
December 15, 2009
HIRC
Stop
Stop
Run
HIRC + LXT
unimplemented
LXT
Run
Run
Run