HT1621 datasheet(12/20 Pages) HOLTEK

12 / 20 page

HT1621

April 21, 2000

OFF command turns the LCD display off by dis-

abling 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.

Command format

The HT1621 can be configured by the S/W set-

ting. There are two mode commands to configure

the HT1621 resources and to transfer the LCD

display data. The configuration mode of the

HT1621 is called command mode, and its com-

mand mode ID is 100. The command mode con-

sists of a system configuration command, a

system frequency selection command, a LCD con-

figuration command, a tone frequency selection

command, a timer/WDT setting command, and

an operating command. The data mode, on the

other hand, includes READ, WRITE, and

READ-MODIFY-WRITE operations. The follow-

ing are the data mode IDs and the command

mode ID:

Operation

Mode

READ

Data

1 1 0

WRITE

Data

1 0 1

READ-MODIFY-WRITE

Data

1 0 1

COMMAND

Command 1 0 0

The mode command should be issued before the

data or command is transferred. If successive

commands have been issued, the command

mode ID, namely 100, can be omitted. While

the system is operating in the non-successive

command or the non-successive address data

mode, the CS pin should be set to "1" and the

previous operation mode will be reset also.

Once the CS pin returns to "0" a new operation

mode ID should be issued first.

Interfacing

Only four lines are required to interface with

the HT1621. The CS line is used to initialize the

serial interface circuit and to terminate the com-

munication between the host controller and the

HT1621. If the CS pin is set to 1, the data and

command issued between the host controller and

the HT1621 are first disabled and then initial-

ized. Before issuing a mode command or mode

switching, a high level pulse is required to initial-

ize the serial interface of the HT1621. The DATA

line is the serial data input/output line. Data to

be read or written or commands to be written

have to be passed through the DATA line. The RD

line is the READ clock input. Data in the RAM

are clocked out on the falling edge of the RD sig-

nal, and the clocked out data will then appear on

the DATA line. It is recommended that the host

controller read in correct data during the interval

between the rising edge and the next falling edge

of the RD signal. The WR line is the WRITE clock

input. The data, address, and command on the

DATA line are all clocked into the HT1621 on the

rising edge of the WR signal. There is an optional

IRQ line to be used as an interface between the

host controller and the HT1621. The IRQ pin can

be selected as a timer output or a WDT overflow

flag output by the S/W setting. The host control-

ler can perform the time base or the WDT func-

tion by being connected with the IRQ pin of the

HT1621.

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