DS1500 Y2KC Watchdog RTC with Nonvolatile Control

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PIN DESCRIPTION

PIN

NAME

FUNCTION

1

SQW

Square-Wave Output. When enabled, the SQW pin outputs a 32.768kHz square wave. If the square

wave (

2

KS

Kickstart Input. This pin is used to wake up a system from an external event, such as a key closure.

The

connect to ground.

3

Battery input for any standard 3V lithium cell or other energy source. Battery voltage must be held

between 2.5V and 3.7V for proper operation. UL recognized to ensure against reverse charging

current when used with a lithium battery. If not used, connect to ground.*

4

Auxiliary battery input for any standard 3V lithium cell or other energy source. Battery voltage must

be held between 2.5V and 3.7V for proper operation. Provides backup power to the device, and

provides power for auxiliary functions. UL recognized to ensure against reverse charging current

when used with a lithium battery. If not used, connect to ground.*

5

CEO

6

CEI

Chip-Enable Input. Input for chip-enable signal for external SRAM.

7

WE

Write-Enable Input. Active-low input that enables DQ0–DQ7 for data input to the device.

8

voltage, the RAM and timekeeping circuits are switched over to the battery.

9

mode.

10

N.C.

No Connect

11

PWR

Power-On Output (Open Drain). This output, if used, is normally connected to power-supply control

circuitry. This pin requires a pullup resistor connected to a positive supply to operate correctly.

12, 13

X1, X2

Connections for a standard 32.768kHz quartz crystal. For greatest accuracy, the DS1500 must be

used with a crystal that has a specified load capacitance of either 6pF or 12.5pF. The crystal select

(CS) bit in control register B is used to select operation with a 6pF or 12.5pF crystal. The crystal is

attached directly to the X1 and X2 pins. There is no need for external capacitors or resistors. An

external 32.768kHz oscillator can also drive the DS1500. In this configuration, the X1 pin is

connected to the external oscillator signal and the X2 pin is floated. For more information about

crystal selection and crystal layout considerations, refer to Application Note 58: Crystal

Considerations with Dallas Real-Time Clocks. See Figure 8.

14

RST

Reset Output (Open Drain). This output, if used, is normally connected to a microprocessor-reset

input. This pin requires a pullup resistor connected to a positive supply to operate correctly. When

RST is active, the device is not accessible.

15

IRQ

Interrupt Output (Open Drain). This output, if used, is normally connected to a microprocessor

interrupt input. This pin requires a pullup resistor connected to a positive supply to operate correctly.

16–20

A4–A0

Address Inputs. Selects one of 17 register locations.

21–23,

25–29

DQ0–DQ7

Data I/O pins for 8-bit parallel data transfer.

24, 31

GND

voltage, the RAM and timekeeping circuits are switched over to the battery.

30

CS

Chip-Select Input. Active-low input to enable the device.

32

OE

Output-Enable Input. Active-low input that enables DQ0–DQ7 for data output from the device