Operating Mode Switching - Holtek HT66F20 Manual

Operating Mode Switching

The device can switch between operating modes dynamically allowing the user to select the best
performance/power ratio for the present task in hand. In this way microcontroller operations that
do not require high performance can be executed using slower clocks thus requiring less operating
current and prolonging battery life in portable applications.
In simple terms, Mode Switching between the NORMAL Mode and SLOW Mode is executed
using the HLCLK bit and CKS2~CKS0 bits in the SMOD register while Mode Switching from the
NORMAL/SLOW Modes to the SLEEP/IDLE Modes is executed via the HALT instruction. When
a HALT instruction is executed, whether the device enters the IDLE Mode or the SLEEP Mode is
determined by the condition of the IDLEN bit in the SMOD register and FSYSON in the WDTC
register.
When the HLCLK bit switches to a low level, which implies that clock source is switched from the
high speed clock source, f
speed clock source will stop running to conserve power. When this happens it must be noted that the
f /16 and f /64 internal clock sources will also stop running, which may affect the operation of other
H H
internal functions such as the TMs and the SIM. The accompanying flowchart shows what happens
when the device moves between the various operating modes.
S L E E P 0
H A L T i n s t r u c t i o n i s e x e c u t e d
f o f f
S Y S
C P U s t o p
I D L E N = 0
f o f f
T B C
f o f f
S U B
W D T & L V D o f f
H A L T i n s t r u c t i o n i s e x e c u t e d
Rev. 2.50
HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
, to the clock source, f
H H
N O R M A L
H A L T i n s t r u c t i o n i s e x e c u t e d
f = f ~ f / 6 4
S Y S H H
f o n
H
C P U r u n
f o n
S Y S
f o n
T B C
f o n
S U B
S L E E P 1
f o f f
S Y S
C P U s t o p
I D L E N = 0
f o f f
T B C
f o n
S U B
W D T o r L V D o n
62
A/D Flash MCU with EEPROM
/2~f /64 or f . If the clock is from the f
H L
I D L E 1
C P U s t o p
I D L E N = 1
F S Y S O N = 1
f o n
S Y S
f o n
T B C
f o n
S U B
H A L T i n s t r u c t i o n i s e x e c u t e d
C P U s t o p
I D L E N = 1
F S Y S O N = 0
S L O W
f = f
S Y S L
f o n
L
C P U r u n
f o n
S Y S
f o n
T B C
f o n
S U B
f o f f
H
, the high
L
I D L E 0
f o f f
S Y S
f o n
T B C
f o n
S U B
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