HT1621
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
Tone output
TIMER command. The CLR WDT or the CLR
TIMER command should be executed prior to
the WDT EN or the TIMER EN command re-
spectively. Before executing the IRQ EN com-
mand the CLR WDT or CLR TIMER command
should be executed first. The CLR TIMER com-
mand 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 issued. After the IRQ output is
disabled the IRQ pin will remain at the floating
state. The IRQ output can be enabled or dis-
abled 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 config-
uration 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 corresponding system commands. At the
power down mode the time base/WDT loses all
its functions.
A simple tone generator is implemented in the
HT1621. The tone generator can output a pair
of differential driving signals on the BZ and BZ,
which are used to generate a single tone. By ex-
ecuting the TONE4K and TONE2K commands
there are two tone frequency outputs
selectable. The TONE4K and TONE2K com-
mands 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 outputs,
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 re-
main 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 configu-
ration. This feature makes the HT1621 suitable
for multiply LCD applications. 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
frequency. The LCD corresponding commands
are summarized in the table.
On the other hand, if an external clock is se-
lected 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 selected,
the HT1621 will continue working until system
power fails or the external clock source is re-
moved. After the system power on, the IRQ will
be disabled.
The bold form of 1 0 0, namely 1 0 0, indicates
the command mode ID. If successive commands
have been issued, the command mode ID except
for the first command, will be omitted. The LCD
11
January 10, 2001
ETC [ ETC ]
