HT48R063B/064B/065B/066B
frequency of 4MHz within a tolerance of 2%. Here only
the OSC1 pin is used, which is shared with I/O pin PA6,
leaving pin PA5 free for use as a normal I/O pin.
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 al-
low a high speed oscillator to be used in conjunction
with a a low speed oscillator, known as the LXT oscilla-
tor. The LXT oscillator is implemented using a 32768Hz
crystal connected to pins OSC1/OSC2. However, for
some crystals, to ensure oscillation and accurate fre-
quency 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 devices the LXT oscillator must be used together
with the HIRC oscillator.
V
D
D
R
O
S
C
P
A
6
/
O
S
C
1
4
7
0
p
F
P
A
5
/
O
S
C
2
External RC Oscillator - ERC
Internal RC Oscillator - HIRC
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.
32768 Hz Crystal Recommended Capacitor Values
·
If the I/O option is selected then the XT1/XT2 pins can
be used as normal I/O pins.
·
If the ²LXT oscillator²is selected then the 32kHz crys-
tal should be connected to the XT1/XT2 pins.
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
I
n
t
e
r
n
a
l
R
C
O
s
c
i
l
l
a
t
o
r
LXTLP Bit
LXT Mode
Quick Start
Low-power
N
o
t
e
:
0
1
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 Idle/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
I
O
C
n
t
e
r
n
a
l
C
1
s
c
i
l
l
a
t
o
r
i
r
c
u
i
t
R
p
3
2
7
6
8
H
z
I
n
t
e
r
n
a
l
R
C
O
s
c
i
l
l
a
t
o
r
T
c
o
i
n
t
e
r
n
a
l
i
r
c
u
i
t
s
C
2
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.
N
o
t
e
:
1
.
R
p
,
C
1
a
n
d
C
2
a
r
e
r
e
q
u
i
r
e
d
.
2
.
A
p
l
t
h
o
u
g
h
n
o
t
s
h
o
w
n
p
i
n
s
h
a
v
e
a
a
r
a
s
i
t
i
c
c
a
p
a
c
i
t
a
n
c
e
o
f
a
r
o
u
n
d
7
p
F
.
External LXT Oscillator
Rev. 1.00
26
April 7, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
