HT46801N-1 Holtek Semiconductor, HT46801N-1 Datasheet - Page 20

• Manufacturer Part Number: HT46801N-1
• Description: (HT4xR01x-1) Small Package 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

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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.
System
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.
System Clock Configurations
There are four system oscillators implemented in this
device, three high speed oscillators and one low speed
oscillator. The high speed oscillators are the external
crystal/ceramic oscillator -- HXT, the external RC oscil-
lator -- ERC and the internal RC oscillator -- HIRC. The
low speed oscillator is the external 32.768 kHz crystal
oscillator -- LXT. The LXT oscillator can be used as the
system oscillator only when the HIRC oscillator is se-
lected as the high speed system oscillator for the de-
vices. Also there is an internal 15kHz RC oscillator
named LIRC oscillator used as the clock source for the
Rev.1.00
External Crystal
External RC
Internal High Speed RC HIRC
External Low Speed
Crystal
Internal Low Speed RC
Oscillator Overview
Crystal/Resonator Oscillator - HXT
Type
Oscillator Types
Name
LIRC
ERC
HXT
LXT
12MHz
12MHz
32768Hz
400kHz~
400kHz~
12MHz
4, 8 or
13kHz
Freq.
OSC1
OSC2
OSC1
OSC1
OSC2
Pins
20
WDT function. More details are described in the accom-
panying sections.
External Crystal/Resonator Oscillator - HXT
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
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.
External RC Oscillator - ERC
Using the ERC oscillator only requires that a resistor,
with a value between 24k
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. Refer to the A.C. Characteris-
tics for more frequency accuracy details. 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.
Crystal Frequency
12MHz
8MHz
4MHz
1MHz
Note: C1 and C2 values are for guidance only.
Crystal Recommended Capacitor Values
Crystal Oscillator C1 and C2 Values
External RC Oscillator - ERC
HT46R01B-1/HT46R01N-1
HT48R01B-1/HT48R01N-1
and 1.5M , is connected
100pF
8pF
8pF
8pF
C1
June 9, 2011
100pF
10pF
10pF
10pF
C2
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