DS1306

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registers is set to a logic 1. Similarly, an alarm is generated every minute when bit 7 of the day, hour, and

minute alarm registers is set to a logic 1. When bit 7 of the day, hour, minute, and seconds alarm registers

is set to a logic 1, an alarm occurs every second.

During each clock update, the RTC compares the Alarm 0 and Alarm 1 registers with the corresponding

clock registers. When a match occurs, the corresponding alarm flag bit in the status register is set to a 1. If

the corresponding alarm interrupt enable bit is enabled, an interrupt output is activated.

Table 2. TIME-OF-DAY ALARM MASK BITS

ALARM REGISTER MASK BITS (BIT 7)

SECONDS

MINUTES

HOURS

DAYS

FUNCTION

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 hours, minutes, and seconds match

0

0

0

0

Alarm day, hours, minutes and seconds match

SPECIAL PURPOSE REGISTERS

The DS1306 has three additional registers (control register, status register, and trickle charger register)

that control the real-time clock, interrupts, and trickle charger.

CONTROL REGISTER (READ 0Fh, WRITE 8Fh)

BIT7

BIT6

BIT5

BIT4

BIT3

BIT2

BIT1

BIT0

0

WP

0

0

0

1Hz

AIE1

AIE0

WP (Write Protect) – Before any write operation to the clock or RAM, this bit must be logic 0. When

high, the write protect bit prevents a write operation to any register, including bits 0, 1, and 2 of the

control register. Upon initial power-up, the state of the WP bit is undefined. Therefore, the WP bit should

be cleared before attempting to write to the device. When WP is set, it must be cleared before any other

control register bit can be written.

1Hz (1Hz Output Enable) – This bit controls the 1Hz output. When this bit is a logic 1, the 1Hz output

is enabled. When this bit is a logic 0, the 1Hz output is high-Z.

AIE0 (Alarm Interrupt Enable 0) – When set to a logic 1, this bit permits the interrupt 0 request flag

AIE1 (Alarm Interrupt Enable 1) – When set to a logic 1, this bit permits the interrupt 1 request flag

(IRQF1) bit in the status register to assert INT1. When the AIE1 bit is set to logic 0, the IRQF1 bit does

not initiate an interrupt signal, and the INT1 pin is set to a logic 0 state.