DS1501/DS1511 Y2KC Watchdog Real-Time Clocks

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The third method of reading the time and date uses the alarm function. The alarm can be configured to activate

once per second, and the time-of-day alarm-interrupt enable bit (TIE) is enabled. The TE bit should always be

enabled. When the

IRQ pin goes active, the time and date information does not change until the next update.

SETTING THE CLOCK

It is recommended to halt updates to the external set of double-buffered RTC registers when writing to the clock.

The (TE) bit should be used as described above before loading the RTC registers with the desired RTC count (day,

date, and time) in 24-hour BCD format. Setting the TE bit to 1 transfers the new values written to the internal RTC

registers and allows normal operation to resume.

CLOCK ACCURACY

The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between

the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Additional

error is added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the

oscillator circuit can result in the clock running fast.

A standard 32.768kHz quartz crystal should be directly connected to the DS1501 X1 and X2 oscillator pins. The

accordingly. An external 32.768kHz oscillator can also drive the DS1501. When using an external oscillator the X2

pin must be left open. The DS1511 contains an embedded crystal and is factory trimmed to be better than ±1

min/month at +25

Refer to Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for detailed information.

Table 2. Register Map

DATA

ADDRESS

B7

B6

B5

B4

B3

B2

B1

B0

FUNCTION

BCD

RANGE

00H

0

10 Seconds

Seconds

Seconds

00–59

01H

0

10 Minutes

Minutes

Minutes

00–59

02H

0

0

10 Hours

Hour

Hours

00–23

03H

0

0

0

0

0

Day

Day

1–7

04H

0

0

10 Date

Date

Date

01–31

05H

EOSC

E32K

BB32

10 Month

Month

Month

01–12

06H

10 Year

Year

Year

00–99

07H

10 Century

Century

Century

00–39

08H

AM1

10 Seconds

Seconds

Alarm Seconds

00–59

09H

AM2

10 Minutes

Minutes

Alarm Minutes

00–59

0AH

AM3

0

10 Hours

Hour

Alarm Hours

00–23

0BH

AM4

Dy/Dt

10 Date

Day/Date

Alarm Day/Date

1–7/1–31

0CH

0.1 Second

0.01 Second

Watchdog

00–99

0DH

10 Second

Second

Watchdog

00–99

0EH

BLF1

BLF2

PRS

PAB

TDF

KSF

WDF

IRQF

Control A

0FH

TE

CS

BME

TPE

TIE

KIE

WDE

WDS

Control B

10H

Extended RAM Address

RAM Address

00–FF

11H

Reserved

12H

Reserved

13H

Extended RAM Data

RAM Data

00–FF

14H-1FH

Reserved

Note: 0 = 0 and are read only.

POWER-UP DEFAULT STATES

These bits are set upon power-up:

EOSC = 0, E32K = 0, TIE = 0, KIE = 0, WDE = 0, and WDS = 0. Unless

otherwise specified, the state of the control/RTC/SRAM bits in the DS1501/DS1511 is not defined upon initial

power application; the DS1501/DS1511 should be properly configured/defined during initial configuration.