HT1621 datasheet(9/21 Pages) HOLTEK

9 / 21 page

HT1621

Rev. 2.60

October 28, 2009

PATENTED

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.

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

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.

The bold form of100, namely 100, 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-

erator. 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 com-

T I M E R E N / D I S

W D T E N / D I S

V D D

I R Q

I R Q E N / D I S

C K

C L R W D T

S y s t e m C l o c k

f = 3 2 k H z

/ 2 5 6

/ 4

W D T

T i m e r / W D T

C l o c k S o u r c e s

/ 2 n

n = 0 ~ 7

Timer and WDT Configurations

Name

Command Code

Function

LCD OFF

100 00000010X

Turn off LCD outputs

LCD ON

100 00000011X

Turn on LCD outputs

BIAS & COM

100 0010abXcX

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

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