HT1621

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7

Command Format

The HT1621 can be configured by the S/W setting . 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 command mode ID is 100. The

command mode consists of a system configuration command, a

system frequency selection command, a LCD configuration

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 following are the data

mode IDS and the command mode ID;

Operation

Mode

ID

Read

Data

110

Write

Data

101

Read-Modify-write

Data

101

Command

Command

100

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

pin should be set to “1” and the previous

operation mode will be reset also. Once the

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

line is used to initialize the serial interface circuit and to terminate

the communication between the host controller and the HT1621. If

the

pin is set to 1, the data and command issued between the

host controller and the HT1621 are first disabled and then initialized.

Before 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

line is the READ clock input Data in the RAM

are clocked out on the falling edge of the

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 between

the rising edge and the next falling edge of the

signal. The

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

signal. There is an optional

line to be

used as an interface between the host controller and the HT1621.

The

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

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 correct 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 table illustrations the suggestion value of capacities (C1, C2)

Crystal Error

Capacity Value

±10ppm

0

~10p

10

~20ppm

10

~20p

Timing Diagrams

READ Mode (Command Code:110)