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System RC Oscillator
Using the external RC network as an oscillator requires that a resistor, with a value between 24k
W
and 1M
W
, is connected between OSC1 and VDD, and a 470pF capacitor is connected to ground.
The generated system clock divided by 4 will be provided on OSC2 as an output which can be
used for external synchronization purposes. Although this is a cost effective oscillator configura-
tion, the oscillation frequency can vary with VDD, temperature and process variations on the chip
itself and is therefore not suitable for applications where timing is critical or where accurate oscilla-
tor frequencies are required. For the value of the external resistor R
OSC
please refer to the Appen-
dix section for typical RC Oscillator vs. Temperature and V
DD
characteristics graphics.
Watchdog Timer Oscillator
The WDT oscillator is a fully self-contained free running on-chip RC oscillator with a typical period
of 65
m
s at 5V requiring no external components. When the device enters the Power Down Mode,
the system clock will stop running but the WDT oscillator continues to free-run and to keep the
Watchdog active. However, to preserve power in certain applications the WDT oscillator can be
disabled via a configuration option.
Power Down Mode and Wake-up
Power Down Mode
All of the Holtek microcontrollers have the ability to enter a Power Down Mode, also known as the
HALT Mode or Sleep Mode. When the device enters this mode, the normal operating current, will
be reduced to an extremely low standby current level. This occurs because when the device en-
ters the Power Down Mode, the system oscillator is stopped which reduces the power consump-
tion to extremely low levels, however, as the device maintains its present internal condition, it can
be woken up at a later stage and continue running, without requiring a full reset. This feature is ex-
tremely important in application areas where the MCU must have its power supply constantly main-
tained to keep the device in a known condition but where the power supply capacity is limited such
as in battery applications.
Entering the Power Down Mode
There is only one way for the device to enter the Power Down Mode and that is to execute the
²
HALT
²
instruction in the application program. When this instruction is executed, the following will oc-
cur:
·
The system oscillator will stop running and the application program will stop at the
²
HALT
²
in-
struction.
·
The Data Memory contents and registers will maintain their present condition.
Chapter 1 Hardware Structure
39
R C O s c i l l a t o r
O S C 1
O S C 2
f
S Y S
/ 4 N M O S O p e n D r a i n
4 7 0 p F
V
D D
R
O S C
Содержание HT48R05A-1
Страница 7: ...vi Cost Effective I O Type MCU...
Страница 8: ...P a r t I Microcontroller Profile Part I Microcontroller Profile 1...
Страница 9: ...2 Cost Effective I O Type MCU...
Страница 52: ...P a r t I I Programming Language Part II Programming Language 45...
Страница 53: ...46 Cost Effective I O Type MCU...
Страница 59: ...52 Cost Effective I O Type MCU...
Страница 90: ...P a r t I I I Development Tools Part III Development Tools 83...
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Страница 101: ...94 Cost Effective I O Type MCU...
Страница 104: ...Appendix Appendix 97...
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Страница 116: ...A p p e n d i x B Package Information Appendix B Package Information 109 B...
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Страница 125: ...Amendments...