HT1621 datasheet(10/21 Pages) HOLTEK

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Timing Diagrams

READ Mode (Command Code:110)

HT1621

Rev. 2.60

October 28, 2009

PATENTED

mands. 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 setting. There

are two mode commands to configure the HT1621 re-

sources and to transfer the LCD display data. The configu-

ration mode of the HT1621 is called command mode, and

its command mode ID is 100. The command mode con-

sists of a system configuration command, a system

frequency selection command, a LCD configuration com-

mand, 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 following 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

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 ad-

dress data mode, the CS pin should be set to

²1² and the

previous operation mode will be reset also. Once the CS

pin returns to

²0² a new operation mode ID should be is-

sued first.

Interfacing

Only four lines are required to interface with the

HT1621. The CS line is used to initialize the serial inter-

face circuit and to terminate the communication 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 initialized. Be-

fore issuing a mode command or mode switching, a high

level pulse is required to initialize 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 signal, 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 be-

tween 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 controller can perform the

time base or the WDT function by being connected with

the IRQ pin of the HT1621.

Crystal Selection

A 32768Hz crystal can be directly connected to the

HT1621 via OSCI and OSCO. In order to obtain the cor-

rect frequency, two additional load capacities (C1, C2)

are needed. The value of the capacity depends on how

accurate the crystal is. We suggest that you can follow

the table, which suggests the value of capacities.The ta-

ble illustrations the suggestion value of capacities (C1,

C2)

Crystal Error

Capacity Value

±10ppm

0~10p

10~20ppm

10~20p

R D

D A T A

W R

0 A 5 A 4 A 3 A 2 A 1 A 0 D 0 D 1 D 2 D 3

M e m o r y A d d r e s s 1 ( M A 1 )

D a t a ( M A 2 )

0 A 5 A 4 A 3 A 2 A 1 A 0 D 0 D 1 D 2 D 3

D a t a ( M A 1 )

M e m o r y A d d r e s s 2 ( M A 2 )

C S

O S C I

O S C O

3 2 7 6 8 H z

C 1

C 2

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