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- 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

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

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.