HT1650(2005) Ver la hoja de datos (PDF) - Holtek Semiconductor
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HT1650 Datasheet PDF : 18 Pages
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W R ,R D 90%
C lo c k
50%
10%
tf
tr
tC L K
tC L K
Figure 1
CS
W R ,R D
C lo c k
50%
tsu 1
tC S
th 1
50%
F ir s t
C lo c k
Last
C lo c k
Figure 3
DB
V DD
GND
W R ,R D
C lo c k
V DD
GND
V DD
GND
V a lid D a ta
50%
ts u
th
50%
Figure 2
HT1650
V DD
GND
GND
Functional Description
System Oscillator
The HT1650 system clock is used to generate the time
base or Watchdog Timer (WDT) clock frequency, LCD
driving clock, and tone frequency. The clock source may
be from an on-chip RC oscillator (32kHz), a crystal oscil-
lator (32.768kHz), or an external 32kHz clock by the
S/W setting. The configuration of the system oscillator is
as shown. After the SYS DIS command is executed, the
system clock will stop and the LCD bias generator will
turn off. That command is available only for the on-chip
RC oscillator or for the crystal oscillator. Once the sys-
tem clock stops, the LCD display will become blank, and
the time base/WDT loses its function as well.
The LCD OFF command is used to turn the LCD bias
generator off. After the LCD bias generator switches off
by issuing the LCD OFF command, using the SYS DIS
command reduces power consumption, thus serving as
a system power down command. But if the external
clock source is chosen as the system clock, using the
SYS DIS command can neither turn the oscillator off nor
carry out the power down mode. The crystal oscillator
option can be applied to connect an external frequency
source of 32kHz to the OSCI pin. In this case, the sys-
tem fails to enter the power down mode, similar to the
case of the external 32kHz clock source operation. At
the initial system power on, the HT1650 is at the SYS
DIS state.
O SCI
O SCO
C r y s ta l O s c illa to r
32768H z
E x te r n a l C lo c k S o u r c e
32kH z
O n - c h ip R C O s c illa to r
32kH z
System Oscillator Configuration
S y s te m
C lo c k
Rev. 1.20
7
November 10, 2005
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