HT1621

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6

Timer and WDT Configurations

The WDT time-out flag output (connect the WDT time-out flag to the

pin). After the TIMER EN command is transferred, the WDT is

disconnected from the

pin, and the output of the time base

generator is connected to the

pin. The WDT can be cleared

by executing 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 executing the

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

pin will stay at a logic low level until the CLR WDT

or the

DIS command is issued. After the

output is

disabled the

pin will remain at the floating state. The

output can be enabled or disabled by executing the

EN or the

DIS command, respectively. The

EN makes the output

of the time base generator or of the WDT time-out flag appear on

the

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

corresponding system commands. At the power down mode the

time base/WDT loses all its functions.

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 selected, the HT1621 will continue working until

system power fails or the external clock source is removed. After the

system power on, the

will be disabled.

Tone Output

A simple tone generator is implemented in the HT1621.The tone

generator can output a pair of differential driving signals on the BZ

and

, which are used to generate a single tone. By executing the

TONE4K and TONE2K commands there are two tone frequency

outputs 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 outputs , namely BZ and

, 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

outputs will remain at low level.

LCD Driver

The HT1621 is a 128 (32x4) 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 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.

The bold form of 100, namely 100, 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 OFF

command turns the LCD display off by disabling the LCD bias

generator. The LCD ON command, on the other hand, turns the

LCD display on by enabling the LCD bias generator. The BIAS and

COM are the LCD panel related commands. Using the LCD related

commands, the HT1621 can be compatible with most types of LCD

panels.

Name

Command Code

Function

LCD OFF

10000000010X

Turn off LCD outputs

LCD ON

10000000011X

Turn on LCD outputs

BIAS & COM

1000010abxcx

C=0:1/2 bias option

C=1: 1/3 bias option

ab=00:2 commons option

ab=01:3 commons option

ab=10:4 commons option