DS1501/DS1511 Y2KC Watchdog Real-Time Clocks

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PIN DESCRIPTION

PIN

DIP, SO

MODULE

TSOP

NAME

FUNCTION

1

1

8

PWR

Active-Low 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.

2, 3

—

9, 10

X1, X2

Connections for Standard 32.768kHz Quartz Crystal. For greatest accuracy, the

DS1501 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 DS1501. 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 9. An enable bit in

the month register controls the oscillator. Oscillator startup time is highly dependent

upon crystal characteristics, PC board leakage, and layout. High ESR and excessive

capacitive loads are the major contributors to long startup times. A circuit using a

crystal with the recommended characteristics and proper layout usually starts within

one second.

4

4

11

RST

Active-Low Reset Output. (Open Drain). This output, if used, is normally connected

to a microprocessor-reset input. This pin requires a pull up resistor connected to a

positive supply to operate correctly. When

RST is active, the device is not accessible.

5

5

12

IRQ

Active-Low 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.

6–10

6–10

13–17

A4–A0

Address Inputs. Selects one of 17 register locations.

11–13,

15–19

11–13,

15–19

18–20,

22–26

DQ0–DQ7

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

14, 21

14

21, 28

GND

When power is applied within the normal limits, the device is fully accessible and

timekeeping circuits are switched over to the battery.

22

22

1

OE

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

the device.

20

20

27

CE

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

23

23

2

SQW

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

wave. If the square wave (

E32K) and battery backup 32kHz (BB32) bits are enabled,

24

24

3

KS

Active-Low Kickstart Input. This pin is used to wake up a system from an external

event, such as a key closure. The

KS pin is normally connected using a pullup

25

—

4

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.*

26

26

5

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. UL

recognized to ensure against reverse charging current when used with a lithium

battery. If not used, connect to ground.*

27

27

6

WE

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

device.

28

28

7

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

—

2, 3, 21,

25

—

N.C.

No Connect

*See “Conditions of Acceptability” at www.maxim-ic.com/TechSupport/QA/ntrl.htm.