IDT1338

REAL-TIME CLOCK WITH BATTERY BACKED NON-VOLATILE RAM

RTC

IDT™ REAL-TIME CLOCK WITH BATTERY BACKED NON-VOLATILE RAM 7

IDT1338

REV J 111009

being PM. In the 24-hour mode, bit 5 is the second 10-hour

bit (20–23 hours). If the 12/24-hour mode select is changed,

the hours register must be re-initialized to the new format.

set of registers. The time information is read from these

secondary registers, while the clock continues to run. This

eliminates the need to re-read the registers in case of an

update of the main registers during a read.

Table 4. Control Register (07H)

The control register controls the operation of the SQW/OUT pin and provides oscillator status.

Bit 7: Output Control (OUT). Controls the output level of the SQW/OUT pin when the square-wave output is disabled. If SQWE

= 0, the logic level on the SQW/OUT pin is 1 if OUT = 1; it is 0 if OUT = 0.

Bit 5: Oscillator Stop Flag (OSF). A logic 1 in this bit indicates that the oscillator has stopped or was stopped for some time

period and can be used to judge the validity of the clock and calendar data. This bit is edge triggered, and is set to logic 1 when

the internal circuitry senses the oscillator has transitioned from a normal run state to a STOP condition. The following are

examples of conditions that may cause the OSF bit to be set:

1) The first time power is applied.

2) The voltage present on VCC and VBAT are insufficient to support oscillation.

3) The CH bit is set to 1, disabling the oscillator.

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

This bit remains at logic 1 until written to logic 0. This bit can only be written to logic 0. Attempting to write OSF to logic 1 leaves

the value unchanged.

Bit 4: Square-Wave Enable (SQWE). When set to logic 1, this bit enables the oscillator output to operate with either VCC or

Bits 1 and 0: Rate Select (RS1 and RS0). These bits control the frequency of the square-wave output when the square-wave

output has been enabled. The table below lists the square-wave frequencies that can be selected with the RS bits.

Table 5. Square Wave Output

Bit #Bit 7Bit 6Bit 5Bit 4Bit 3Bit 2Bit 1Bit 0

Name

OUT

0

OSF

SQWE

0

0

RS1

RS0

POR

10110011

OUT

RS1

RS0

SQW Output

SQWE

X0

0

1 Hz

1

X

0

1

4.096 kHz

1

X

1

0

8.192 kHz

1

X

1

1

32.768 kHz

1

0X

X

0

0

1X

X

1

0