RS5C372A-E2-F datasheet(42/57 Pages) RICOH | I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC

Part No.	RS5C372A-E2-F

Description	I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC

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Manufacturer	RICOH [RICOH electronics devices division]

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RS5C372A/B

41

3. Oscillator Halt Sensing

Oscillation halt can be sensed through monitoring the XSTP bit with preceding setting of the XSTP bit to 0 by

writing data to the control register 2. Upon oscillator halt sensing, the XSTP bit is switched from 0 to 1. This

function can be applied to judge clock data validity. When the XSTP bit is 1, XSL , F6 to F0, CT2, CT1, CT0, AALE,

BALE, SL2, SL1, CLEN and TEST bits are reset to 0.

1) The XSTP bit is set to 1 upon power-on from 0V.

Note that any instantaneous power disconnection may cause operation failure.

2) Once oscillation halt has been sensed, the XSTP bit is held at 1 even if oscillation is restarted.

Considerations in Use of XSTP Bit

Ensure error-free oscillation halt sensing by preventing the following events:

1) Instantaneous disconnection of VDD

2) Condensation on the crystal oscillator

3) Generation of noise on the PCB in the crystal oscillator

4) Application of voltage exceeding prescribed maximum ratings to the individual pins of the IC.

In particular, note that the XSTP bit may fail to be set to 0 in the presence of any applied supply voltage as

illustrated below in such events as backup battery installation. Further, give special considerations to

prevent excessive chattering in the oscillation halt sensing circuit.

VDD

4. INTRA Output and INTRB Output Pins (RS5C372A), INTR Output Pin (RS5C372B)

4.1 INTRA Output and INTRB Output Pins (RS5C372A)

The following three output wave forms can be output from the INTRA or the INTRB pin.

1) Alarm interrupt

When a registered time for alarm (such as day-of-the-week, hour or minute) coincide with calendar counter

(suchas day-of-the-week, hour or minute) interrupt to the CPU are requested with the output pin being on

(“L”). Alarm interrupt consists of Alarm_A and Alarm_B, both have equivalent functions.

2) Periodic interrupt

Outputs an output wave form selected by setting the periodic interrupt frequency select bit. Wave forms

include pulse mode and level mode.

3) 32-kHz clock output

Clock pulses generated in the oscillation circuit are output as they are.

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