Pad Description

Pad No.

Pad Name

I/O

Function

1CS

I

Chip selection input with pull-high resistor

When the CS is logic high, the data and command read from or

written to the HT1621 are disabled. The serial interface circuit

is also reset. But if CS is at logic low level and is input to the CS

pad, the data and command transmission between the host con-

troller and the HT1621 are all enabled.

2RD

I

READ clock input with pull-high resistor

Data in the RAM of the HT1621 are clocked out on the falling

edge of the RD signal. The clocked out data will appear on the

DATA line. The host controller can use the next rising edge to

latch the clocked out data.

3WR

I

WRITE clock input with pull-high resistor

Data on the DATA line are latched into the HT1621 on the ris-

ing edge of the WR signal.

4

DATA

I/O Serial data input/output with pull-high resistor

5

VSS

¾

Negative power supply, ground

7

OSCI

I

The OSCI and OSCO pads are connected to a 32.768kHz crystal

in order to generate a system clock. If the system clock comes

from an external clock source, the external clock source should

be connected to the OSCI pad. But if an on-chip RC oscillator is

selected instead, the OSCI and OSCO pads can be left open.

6

OSCO

O

8

VLCD

I

LCD power input

9

VDD

¾

Positive power supply

10

IRQ

O

Time base or WDT overflow flag, NMOS open drain output

11, 12

BZ, BZ

O

2kHz or 4kHz tone frequency output pair

13~16

COM0~COM3

O

LCD common outputs

48~17

SEG0~SEG31

O

LCD segment outputs

Absolute Maximum Ratings

Supply Voltage.................................-0.3V~5.5V

Storage Temperature....................-50

Operating Temperature..................-25

Note: These are stress ratings only. Stresses exceeding the range specified under Absolute Maxi-

mum Ratings may cause substantial damage to the device. Functional operation of this de-

vice at other conditions beyond those listed in the specification is not implied and prolonged

exposure to extreme conditions may affect device reliability.

HT1621

6

April 21, 2000