BU9873 Datasheet, PDF (24/40 Pages) Rohm – I2C BUS Serial Interface RTC with High-precision Oscillation Adjustment

BU9873
Datasheet
9. Oscillation Halt Sensing Function
This IC has a built-in oscillation halt detection circuit, and store the status in XSTP bit (internal address Fh). If initial power on
from 0V or supply voltage drops without back-up battery, the XSTP bit will be set to “1” automatically. This function can be
applied to judge clock data validity.
XSTP
0
1
Oscillator Halt Sensing Bit
Ordinary oscillation
Oscillator halt sensing
Description
Default
When oscillation is halted after initial power on from 0V or supply voltage drops, the bit will be set to“1” and remain to be
“1”even if oscillation is restarted. This bit may be used to judge validity of clock and calendar data after power on or supply
voltage drops. The XSTP bit can be written to “0” during ordinary oscillation.
When this bit is set to“1”, F₆～F₀, CT₂～CT₀, AALE, BALE, CLENB bits will be reset to “0”. INTRB output will stop and the
32KOUT will output 32-kHz clock pulses.
In order to prevent invalid detection of oscillation halt, the points should be noted as the following.
(1) Instantaneous disconnection of V_DD
(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
10. 32-kHz Clock Output Function
The IC can generate clock pulses of 32-kHz from the 32KOUT pin.
When power on (XSTP=1), 32-kHz clock pulses are output from 32KOUT, which is CMOS push-pull output. The pin is
changed to be high impedance by setting the CLENB (internal address Fh) bit to “1”.
CLENB
0
1
32-kHz Clock Output Bit
32-kHz clock output enabled
32-kHz clock output disabled
Description
Default
By setting this is bit to “0”, outputting clock pulses with the same frequency of crystal oscillator is enabled. 32-kHz clock
output will not be affected from settings in the clock adjustment register.
The timing of 32KOUT with CLENB control is shown below.
CLENB bit
32KOUT pin
MAX. 76.3s
MAX. 76.3s
Figure 27. Output timing between 32KOUT and CLENB bit
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