HT1621 datasheet(8/21 Pages) HOLTEK

8 / 21 page

HT1621

Rev. 2.60

October 28, 2009

PATENTED

Functional Description

Display Memory

- RAM

The static display memory (RAM) is organized into 32

´4

bits and stores the displayed data. The contents of the

RAM are directly mapped to the contents of the LCD

driver. Data in the RAM can be accessed by the READ,

WRITE, and READ-MODIFY-WRITE commands. The

following is a mapping from the RAM to the LCD pattern:

System Oscillator

The HT1621 system clock is used to generate the time

base/Watchdog Timer (WDT) clock frequency, LCD

driving clock, and tone frequency. The source of the

clock may be from an on-chip RC oscillator (256kHz), a

crystal oscillator (32.768kHz), or an external 256kHz

clock by the S/W setting. The configuration of the sys-

tem 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, however, avail-

able only for the on-chip RC oscillator or for the crystal

oscillator. Once the system clock stops, the LCD display

will become blank, and the time base/WDT lose its func-

tion 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, 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 in the external 256kHz clock source operation. At

the initial system power on, the HT1621 is at the SYS

DIS state.

Time Base and Watchdog Timer (WDT)

The time base generator is comprised by an 8-stage

count-up ripple counter and is designed to generate an

accurate time base. The watch dog timer (WDT), on the

other hand, is composed of an 8-stage time base gener-

ator along with a 2-stage count-up counter, and is de-

signed to break the host controller or other subsystems

from abnormal states such as unknown or unwanted

jump, execution errors, etc. The WDT time-out will result

in the setting of an internal WDT time-out flag. The out-

puts of the time base generator and of the WDT time-out

flag can be connected to the IRQ output by a command

option. There are totally eight frequency sources avail-

able for the time base generator and the WDT clock.

The frequency is calculated by the following equation.

fWDT =

32kHz

where the value of n ranges from 0 to 7 by command op-

tions. The 32kHz in the above equation indicates that

the source of the system frequency is derived from a

crystal oscillator of 32.768kHz, an on-chip oscillator

(256kHz), or an external frequency of 256kHz.

If an on-chip oscillator (256kHz) or an external 256kHz

frequency is chosen as the source of the system fre-

quency, the frequency source is by default prescaled to

32kHz by a 3-stage prescaler. Employing both the time

base generator and the WDT related commands, one

should be careful since the time base generator and

WDT share the same 8-stage counter. For example, in-

voking the WDT DIS command disables the time base

generator whereas executing the WDT EN command

not only enables the time base generator but activates

the WDT time-out flag output (connect the WDT

S E G 0

S E G 1

S E G 2

S E G 3

S E G 3 1

C O M 0

C O M 1

C O M 2

C O M 3

D 3

D 2

D 1

D 0

D a t a

A d d r

3 1

A d d r e s s 6 b i t s

( A 5 , A 4 , . . . , A 0 )

D a t a 4 b i t s

( D 3 , D 2 , D 1 , D 0 )

RAM Mapping

1 / 8

O S C I

O S C O

C r y s t a l O s c i l l a t o r

3 2 7 6 8 H z

E x t e r n a l C l o c k S o u r c e

2 5 6 k H z

O n - c h i p R C O s c i l l a t o r

2 5 6 k H z

S y s t e m

C l o c k

System Oscillator Configuration

HT1621 Datenblatt(PDF) 8 Page - Holtek Semiconductor Inc

HT1621 Datenblatt(HTML) 8 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Datenblatt Download

Link URL