Rainbow Electronics DS1511 - Manual (Page 13)

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
crystal selected for use should have a specified load capacitance (C
L
) 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
° C.
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.