HT46R01B/02B/01N/02N
HT48R01B/02B/01N/02N
Internal RC Oscillator - HIRC
C2 should be selected in consultation with the crystal or
resonator manufacturer¢s specification. The external
parallel feedback resistor, RP, is required. For the de-
vice the LXT oscillator must be used together with the
HIRC oscillator.
The internal RC oscillator is a fully integrated system os-
cillator requiring no external components. The internal
RC oscillator has three fixed frequencies of either
4MHz, 8MHz or 12MHz. Device trimming during the
manufacturing process and the inclusion of internal fre-
quency 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 either 3V or
5V and at a temperature of 25 degrees, the fixed oscilla-
tion frequency of 4MHz, 8MHz or 12MHz will have a tol-
erance within 2%. Note that if this internal system clock
option is selected, as it requires no external pins for its
operation, I/O pins PA5 and PA6 are free for use as nor-
mal I/O pins.
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.
32768Hz 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.
P
P
A
A
5
6
/
/
O
O
S
S
C
C
2
1
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LXTLP Bit
LXT Mode
Quick Start
Low-power
0
1
N
o
P
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A
:
5
/
P
A
6
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Internal RC Oscillator - HIRC
External 32768Hz Crystal Oscillator - LXT
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.
When the microcontroller enters the Sleep Mode, the
system clock is switched off to stop microcontroller ac-
tivity 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. However, for some
crystals, to ensure oscillation and accurate frequency
generation, it is necessary to add two small value exter-
nal capacitors, C1 and C2. The exact values of C1 and
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.
I
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Internal Low Speed Oscillator - LIRC
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R
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3
2
7
6
8
H
The LIRC is a fully self-contained free running on-chip
RC oscillator with a typical frequency of 13kHz at 5V re-
quiring no external components. When the device en-
ters the 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 cer-
tain applications the LIRC can be disabled via a configu-
ration option.
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External LXT Oscillator
Rev.1.10
21
February 12, 2010
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
