Rainbow-electronics DS1511 Manual de usuario descargar pdf (Pagina 13)

DS1501/DS1511 Y2KC Watchdog Real-Time Clocks

13 of 20

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

crystal selected for use should have a specified load capacitance (C

) of either 6pF or 12.5pF, and the CS bit set

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.

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