HT46R01B/02B/01N/02N
HT48R01B/02B/01N/02N
Oscillator
Various oscillator options offer the user a wide range of
functions according to their various application require-
ments. The flexible features of the oscillator functions
ensure that the best optimisation can be achieved in
terms of speed and power saving. Oscillator selections
and operation are selected through a combination of
configuration options and registers.
most resonator types, to ensure oscillation and accurate
frequency 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.
Crystal Oscillator C1 and C2 Values
Crystal Frequency
12MHz
C1
8pF
C2
System Oscillator Overview
10pF
10pF
10pF
100pF
8MHz
8pF
In addition to being the source of the main system clock
the oscillators also provide clock sources for the Watch-
dog Timer and Time Base functions. External oscillators
requiring some external components as well as a two
fully integrated internal oscillators, requiring no external
components, are provided to form a wide range of both
fast and slow system oscillators.
4MHz
8pF
1MHz
100pF
Note: C1 and C2 values are for guidance only.
Crystal Recommended Capacitor Values
External RC Oscillator - ERC
Type
Name
Freq.
Using the ERC oscillator only requires that a resistor,
with a value between 24kW and 1.5MW, is connected
between OSC1 and VDD, and a capacitor is connected
between OSC and ground, providing a low cost oscilla-
tor configuration. It is only the external resistor that de-
termines the oscillation frequency; the external
capacitor has no influence over the frequency and is
connected for stability purposes only. 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 resistance/frequency ref-
erence point, it can be noted that with an external 120K
resistor connected and with a 5V voltage power supply
and temperature of 25 degrees, the oscillator will have a
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.
400kHz~
12MHz
External Crystal
HXT
400kHz~
12MHz
External RC
ERC
4, 8 or
Internal High Speed RC
HIRC
12MHz
External Low Speed Crystal
Internal Low Speed RC
LXT
32768Hz
13kHz
LIRC
Oscillator Types
System Clock Configurations
There are five system oscillators. Three high speed os-
cillators and two low speed oscillators. The high speed
oscillators are the external crystal/ceramic oscillator -
HXT, the external - ERC, and the internal RC oscillator -
HIRC. The two low speed oscillator are the external
32768Hz oscillator - LXT and the internal 13kHz
(VDD=5V) oscillator - LIRC.
V
D
D
External Crystal/Resonator Oscillator - HXT
R
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S
C
The simple connection of a crystal across OSC1 and
OSC2 will create the necessary phase shift and feed-
back for oscillation. However, for some crystals and
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External RC Oscillator - ERC
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Crystal/Resonator Oscillator - HXT
Rev.1.10
20
February 12, 2010
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
