HT45R22E Holtek Semiconductor, HT45R22E Datasheet - Page 22

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HT45R22E

Manufacturer Part Number
HT45R22E
Description
Remote Type 8-bit OTP MCU
Manufacturer
Holtek Semiconductor
Datasheet
External RC Oscillator - ERC
Using the ERC oscillator only requires that a resistor,
with a value between 24k and 120k , is connected be-
tween OSC1 and VDD, and a capacitor is connected be-
tween OSC1 and ground, providing a low cost oscillator
configuration. It is only the external resistor that deter-
mines 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 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 resistance/frequency reference point, it
can be noted that with an external 120K resistor con-
nected and with a 3V voltage power supply and temper-
ature 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.
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
4095kHz. Device trimming during the manufacturing
process and the inclusion of internal frequency compen-
sation 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 and at a tem-
perature of 25 degrees, the fixed oscillation frequency of
4095kHz will have a tolerance 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 normal I/O pins.
Rev. 1.00
Crystal Frequency
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
100pF
8pF
C1
100pF
10pF
C2
22
External 32768Hz Crystal Oscillator - LXT
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
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
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
C2 should be selected in consultation with the crystal or
resonator manufacturer s specification. The external
parallel feedback resistor, Rp, is required. The LXT os-
cillator must be used together with the HIRC oscillator.
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.
32768 Hz Crystal Recommended Capacitor Values
Crystal Frequency
32768Hz
Note: 1. C1 and C2 values are for guidance only.
2. R
LXT Oscillator C1 and C2 Values
Internal RC Oscillator - HIRC
P
=5M~10M is recommended.
External LXT Oscillator
8pF
C1
HT45R22E
March 17, 2010
www.DataSheet4U.com
10pF
C2

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