HT1621
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Timer and WDT Configurations
not only enables the time base generator but activates
the WDT time-out flag output (connect the WDT
time-out flag to the IRQ pin). After the TIMER EN com-
mand is transferred, the WDT is disconnected from the
IRQ pin, and the output of the time base generator is con-
nected to the IRQ pin. The WDT can be cleared by execut-
ing the CLR WDT command, and the contents of the time
base generator is cleared by executing the CLR WDT or
the CLR TIMER command. The CLR WDT or the CLR
TIMER command should be executed prior to the WDT
EN or the TIMER EN command respectively. Before ex-
ecuting the IRQ EN command the CLR WDT or CLR
TIMER command should be executed first. The CLR
TIMER command has to be executed before switching
from the WDT mode to the time base mode. Once the
WDT time-out occurs, the IRQ pin will stay at a logic low
level until the CLR WDT or the IRQ DIS command is is-
sued. After the IRQ output is disabled the IRQ pin will re-
main at the floating state. The IRQ output can be
enabled or disabled by executing the IRQ EN or the IRQ
DIS command, respectively. The IRQ EN makes the
output of the time base generator or of the WDT time-out
flag appear on the IRQ pin. The configuration of the time
base generator along with the WDT are as shown. In the
case of on-chip RC oscillator or crystal oscillator, the
power down mode can reduce power consumption
since the oscillator can be turned on or off by the corre-
sponding system commands. At the power down mode
the time base/WDT loses all its functions.
power fails or the external clock source is removed. Af-
ter the system power on, the IRQ will be disabled.
Tone Output
A simple tone generator is implemented in the HT1621.
The tone generator can output a pair of differential driv-
ing signals on the BZ and BZ, which are used to gener-
ate a single tone. By executing the TONE4K and
TONE2K commands there are two tone frequency out-
puts selectable. The TONE4K and TONE2K commands
set the tone frequency to 4kHz and 2kHz, respectively.
The tone output can be turned on or off by invoking the
TONE ON or the TONE OFF command. The tone out-
puts, namely BZ and BZ, are a pair of differential driving
outputs used to drive a piezo buzzer. Once the system is
disabled or the tone output is inhibited, the BZ and the
BZ outputs will remain at low level.
LCD Driver
The HT1621 is a 128 (32´4) pattern LCD driver. It can be
configured as 1/2 or 1/3 bias and 2 or 3 or 4 commons of
LCD driver by the S/W configuration. This feature
makes the HT1621 suitable for multiply LCD applica-
tions. The LCD driving clock is derived from the system
clock. The value of the driving clock is always 256Hz even
when it is at a 32.768kHz crystal oscillator frequency, an
on-chip RC oscillator frequency, or an external fre-
quency. The LCD corresponding commands are sum-
marized in the table.
On the other hand, if an external clock is selected as the
source of system frequency the SYS DIS command
turns out invalid and the power down mode fails to be
carried out. That is, after the external clock source is se-
lected, the HT1621 will continue working until system
The bold form of 1 0 0, namely 1 0 0, indicates the com-
mand mode ID. If successive commands have been is-
sued, the command mode ID except for the first
command, will be omitted. The LCD OFF command
turns the LCD display off by disabling the LCD bias gen-
Name
LCD OFF
Command Code
1 0 0 0 0 0 0 0 0 1 0 X
1 0 0 0 0 0 0 0 0 1 1 X
Function
Turn off LCD outputs
LCD ON
Turn on LCD outputs
c=0: 1/2 bias option
c=1: 1/3 bias option
BIAS & COM
1 0 0 0 0 1 0 a b X c X
ab=00: 2 commons option
ab=01: 3 commons option
ab=10: 4 commons option
Rev. 1.30
8
August 6, 2003
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
