HT56R22 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT56R22' PDF : 134 Pages View PDF
HT56R22/HT56R23/HT56R24/HT56R25/HT56R26
Wake-up Function Register - PAWK
When the microcontroller enters the Idle/Sleep Mode,
various methods exist to wake the device up and con-
tinue with normal operation. One method is to allow a
falling edge on the I/O pins to have a wake-up function.
This register is used to select which Port A I/O pins are
used to have this wake-up function.
Pull-high Registers -
PAPU, PBPU, PCPU, PDPU, PEPU, PFPU, PGPU
The I/O pins, if configured as inputs, can have internal
pull-high resistors connected, which eliminates the need
for external pull-high resistors. This register selects which
I/O pins are connected to internal pull-high resistors.
Software COM Register - SCOMC
The pins PB0~PB3 on Port B can be used as SCOM
lines to drive an external LCD panel. To implement this
function, the SCOMC register is used to setup the cor-
rect bias voltages on these pins.
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 Oscillator Overview
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.
Type
External Crystal
External RC
Internal High
Speed RC
Name
HXT
ERC
HIRC
Freq.
400kHz~
12MHz
400kHz~
12MHz
4, 8 or 12MHz
Pins
OSC1/
OSC2
OSC1
¾
External Low
Speed Crystal
Internal Low
Speed RC
LXT
LIRC
32768Hz
32kHz
¾
XT1/
XT2*
¾
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 32kHz oscilla-
tor - LIRC.
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.
For oscillator stability and to minimise the effects of
noise and crosstalk, it is important to ensure that the
crystal and any associated resistors and capacitors
along with inter connecting lines are all located as close
to the MCU as possible.
C1
O SC1
In te r n a l
O s c illa to r
C ir c u it
Rf
R P1
T o in te r n a l
C2
O SC2
c ir c u its
N o te : 1 . R p is n o r m a lly n o t r e q u ir e d . 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 O S C 1 /O S C 2 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 .
Crystal/Resonator Oscillator - HXT
Crystal Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
12MHz
¾
¾
8MHz
¾
¾
4MHz
¾
¾
1MHz
¾
¾
455kHz (see Note 2)
10pF
10pF
Note: 1. C1 and C2 values are for guidance only.
2. XTAL mode configuration option: 455kHz.
3. RP1=5MW~10MW is recommended.
Crystal Recommended Capacitor Values
Rev. 1.30
28
December 26, 2014
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