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HT66F03 View Datasheet(PDF) - Holtek Semiconductor

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HT66F03 Datasheet PDF : 139 Pages
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HT66F03/HT66F04/HT68F03/HT68F04
system clock option is selected, as it requires no exter-
nal pins for its operation, I/O pins PA6 and PA5 are free
for use as normal I/O pins or external 32.768 kHz crystal
oscillator (LXT) pins.
External 32.768kHz Crystal Oscillator - LXT
The External 32.768kHz Crystal System Oscillator is
one of the low frequency oscillator choices, which is se-
lected via configuration option. This clock source has a
fixed frequency of 32.768kHz and requires a 32.768kHz
crystal to be connected between pins OSC1 and OSC2.
The external resistor and capacitor components con-
nected to the 32.768kHz crystal are necessary to pro-
vide oscillation. For applications where precise
frequencies are essential, these components may be
required to provide frequency compensation due to dif-
ferent crystal manufacturing tolerances. During
power-up there is a time delay associated with the LXT
oscillator waiting for it to start-up.
When the microcontroller enters the SLEEP or IDLE
Mode, the system clock is switched off to stop
microcontroller activity and to conserve power. How-
ever, in many microcontroller applications it may be nec-
essary to keep the internal timers operational even
when the microcontroller is in the SLEEP or IDLE Mode.
To do this, another clock, independent of the system
clock, must be provided.
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 ex-
act values of C1 and C2 should be selected in consulta-
tion with the crystal or resonator manufacturer¢s
specification. The external parallel feedback resistor,
Rp, is required.
Some configuration options determine if the OSC1 and
OSC2 pins are used for the LXT oscillator or as I/O pins.
· If the LXT oscillator is not used for any clock source,
the OSC1 and OSC2 pins can be used as normal I/O
pins.
· If the LXT oscillator is used for any clock source, the
32.768kHz crystal should be connected to the OSC1
and OSC2 pins.
C1
3 2 .7 6 8
kH z
C2
O SC1
Rp
O SC2
In te r n a l
O s c illa to r
C ir c u it
T o in te r n a l
c ir c u its
N o te : 1 . R p , C 1 a n d C 2 a r e r e q u ir e d .
2 . A lth o u g h n o t s h o w n p in s h a v e a
p a r a s itic c a p a c ita n c e o f a r o u n d 7 p F .
External LXT Oscillator
LXT Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
32.768kHz
10pF
10pF
Note: 1. C1 and C2 values are for guidance only.
2. RP=5M~10MW is recommended.
32.768kHz 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 TBC
register.
LXTLP Bit
0
1
LXT Mode
Quick Start
Low-power
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 32kHz Oscillator - LIRC
The Internal 32kHz System Oscillator is one of the low
frequency oscillator choices, which is selected via con-
figuration 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 en-
sure that the influence of the power supply voltage, tem-
perature 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%.
Rev. 1.00
29
April 16, 2010
 

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