IDT1339

RTC

IDT®

9

IDT1339

REV K 032910

Table 5. SQW/INT Output

Bit 2: Interrupt Control (INTCN).

This bit controls the relationship between the two alarms and the interrupt output

pins. When the INTCN bit is set to logic 1, a match between the timekeeping registers and the alarm 1 or alarm 2

registers activate the SQW/INT pin (provided that the alarm is enabled). When the INTCN bit is set to logic 0, a

square wave is output on the SQW/INT pin. This bit is set to logic 0 when power is first applied.

Bit 1: Alarm 2 Interrupt Enable (A2IE).

When set to a logic 1, this bit permits the Alarm 2 Flag (A2F) bit in the

status register to assert SQW/INT (when INTCN = 1). When the A2IE bit is set to logic 0 or INTCN is set to logic 0,

the A2F bit does not initiate an interrupt signal. The A2IE bit is disabled (logic 0) when power is first applied.

Bit 0: Alarm 1 Interrupt Enable (A1IE).

When set to logic 1, this bit permits the Alarm 1 Flag (A1F) bit in the status

register to assert SQW/INT (when INTCN = 1). When the A1IE bit is set to logic 0 or INTCN is set to logic 0, the A1F

bit does not initiate an interrupt signal. The A1IE bit is disabled (logic 0) when power is first applied.

Status Register (0Fh)

Bit 7: Oscillator Stop Flag (OSF).

A logic 1 in this bit indicates that the oscillator either is stopped or was stopped

for some period of time and may be used to judge the validity of the clock and date data. This bit is edge triggered

and is set to logic 1 when the oscillator stops. The following are examples of conditions that can cause the OSF bit

to be set:

1) The first time power is applied.

3) The EOSC bit is turned off.

4) External influences on the crystal (e.g., noise, leakage, etc.).

This bit remains at logic 1 until written to logic 0. This bit can only be written to a logic 0.

Bit 1: Alarm 2 Flag (A2F).

A logic 1 in the Alarm 2 Flag bit indicates that the time matched the alarm 2 registers. If

the A2IE bit is a logic 1 and the INTCN bit is set to a logic 1, the SQW/INT pin is also asserted. A2F is cleared when

written to logic 0. This bit can only be written to logic 0. Attempting to write to logic 1 leaves the value unchanged.

Bit 0: Alarm 1 Flag (A1F).

A logic 1 in the Alarm 1 Flag bit indicates that the time matched the alarm 1 registers. If

the A1IE bit is a logic 1 and the INTCN bit is set to a logic 1, the SQW/INT pin is also asserted. A1F is cleared when

written to logic 0. This bit can only be written to logic 0. Attempting to write to logic 1 leaves the value unchanged.

INTCN

RS2

RS1

SQW/INT Output

A2IE

A1IE

0

0

0

1 Hz

X

X

0

0

1

4.096 kHz

X

X

0

1

0

8.192 kHz

X

X

0

1

1

32.768 kHz

X

X

1

X

X

A1F

0

1

1

X

X

A2F

1

0

1

X

X

A2F + A1F

1

1

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

OSF

0

0

0

0

0

A2F

A1F