DS1670
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CLOCK, CALENDAR, AND ALARM
The time and calendar information is accessed by reading/writing the appropriate register bytes. Note that
some bits are set to 0. These bits will always read 0 regardless of how they are written. Also note that
registers 0 Fh to 7 Fh are reserved. These registers will always read 0 regardless of how they are written.
The contents of the time, calendar, and alarm registers are in the Binary-Coded Decimal (BCD) format.
The DS1670 can run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the
12-hour or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5
is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the second 10-hour bit (20-23
hours).
The DS1670 also contains a time of day alarm. The alarm registers are located in registers 07h to 0 Ah.
Bit 7 of each of the alarm registers are mask bits (see Table 1). When all of the mask bits are logic 0, an
alarm will occur once per week when the values stored in timekeeping registers 00h to 03h match the
values stored in the time of day alarm registers. An alarm will be generated every day when mask bit of
the day alarm register is set to 1. An alarm will be generated every hour when the day and hour alarm
mask bits are set to 1. Similarly, an alarm will be generated every minute when the day, hour, and minute
alarm mask bits are set to 1. When day, hour, minute, and seconds alarm mask bits are set to 1, an alarm
will occur every second.
TIME OF DAY ALARM BITS Table 1
ALARM REGISTER MASK BITS (BIT 7)
SECONDS MINUTES HOURS DAYS
DESCRIPTION
1 1 1 1 Alarm once per second.
0 1 1 1 Alarm when seconds match.
0 0 1 1 Alarm when minutes and seconds match
0 0 0 1 Alarm when hours, minutes and seconds match.
0 0 0 0 Alarm when day, hours, minutes and seconds.
SPECIAL PURPOSE REGISTERS
The DS1670 has two additional registers (control register and status register) that control the real-time
clock and interrupts.
CONTROL REGISTER
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
EOSC
WP AIS1 AIS0 0 0 0 AIE
EOSC (Enable Oscillator). This bit when set to logic 0 will start the oscillator. When this bit is set to a
logic 1, the oscillator is stopped and the DS1670 is placed into a low-power standby mode with a current
drain of less than 200nA when in battery-backup mode. When the DS1670 is powered by V
CC
, the
oscillator is always on regardless of the status of the
EOSC bit; however, the real-time clock is
incremented only when
EOSC
is a logic 0.
WP (Write Protect). Before any write operation to the real time clock or any other registers, this bit
must be logic 0. When high, the write-protect bit prevents a write operation to any register.
