IDT1337

RTC

8

IDT1337

REV J 111009

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 registers

activate the INTA pin (provided that the alarm is enabled) and a match between the timekeeping registers and the

alarm 2 registers activates the SQW/INTB pin (provided that the alarm is enabled). When the INTCN bit is set to

logic 0, a square wave is output on the SQW/INTB 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 INTA (when INTCN = 0) or to assert SQW/INTB (when INTCN = 1). When the A2IE bit 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 INTA. When the A1IE bit is set to logic 0, the A1F bit does not initiate the INTA 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 calendar data. This bit is is set to logic

1 anytime 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.

2) The voltage present on VCC is insufficient to support oscillation.

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.

This flag can be used to generate an interrupt on either INTA or SQW/INTB depending on the status of the INTCN

bit in the control register. If the INTCN bit is set to logic 0 and A2F is at logic 1 (and A2IE bit is also logic 1), the INTA

pin goes low. If the INTCN bit is set to logic 1 and A2F is logic 1 (and A2IE bit is also logic 1), the SQW/INTB pin

goes low. 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 also a logic 1, the INTA pin goes low. 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.

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

OSF

00000

A2F

A1F