HT56R24 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT56R24' PDF : 134 Pages View PDF
HT56R22/HT56R23/HT56R24/HT56R25/HT56R26
External RC Oscillator - ERC
Using the ERC oscillator only requires that a resistor,
with a value between 47kW 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 150kW
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 PC0,
leaving pin PC1 free for use as a normal I/O pin.
For oscillator stability and to minimise the effects of
noise and crosstalk, it is important to locate the capaci-
tor and resistoras close to the MCU as possible.
V DD
R O SC
470pF
P C 1 /O S C 1
P C 0 /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
P C 1 /O S C 2
P C 0 /O S C 1
In te rn a l R C
O s c illa to r
N o te : P C 0 /P C 1 u s e d a s n o rm a l I/O s
Internal RC Oscillator - HIRC
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 PC1 and PC0 are free for use as nor-
mal I/O pins.
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 low speed oscillator, known as the LXT oscillator to be
used. The LXT oscillator is implemented using a
32768Hz crystal connected to pins. 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, RP2, is required.
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
32768H z
R P2
In te r n a l
O s c illa to r
C ir c u it
In te rn a l R C
O s c illa to r
T o in te r n a l
c ir c u its
C2
N o te : 1 . R p , 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 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 .
External 32768Hz Crystal Oscillator - LXT
LXT Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
32768Hz
8pF
10pF
Note: 1. C1 and C2 values are for guidance only.
2. RP2=5M~10MW is recommended.
32768 Hz Crystal Recommended Capacitor Values
For the devices, a configuration option determines if the
XT1/XT2 pins are used for the LXT oscillator or as I/O
pins.
· 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 32768Hz
crystal should be connected to the XT1/ XT2 pins.
Rev. 1.30
29
December 26, 2014
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