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Page - 5 MQ372-02
8. Use Methods
8.1. Overview of Functions
1) Clock functions
This function is used to set and read out month, day, hour, date, minute, second, and year (last two digits) data.
Any (two-digit) year that is a multiple of 4 is treated as a leap year and calculated automatically as such until the year
2099.
∗ For details, see "8.2. Description of Registers".
2) Fixed-cycle interrupt generation function
The fixed-cycle timer interrupt generation function generates an interrupt event periodically at any fixed cycle set
between 244.14 µs and 4095 minutes.
When an interrupt event is generated, the /INT pin goes to low level ("L") and "1" is set to the TF bit to report that an
event has occurred. (However, when a fixed-cycle timer interrupt event has been generated, low-level output from the
/INT pin occurs only when the value of the control register's TIE bit is "1". Up to 7.8 ms after the interrupt occurs, the
/INT status is automatically cleared (/INT status changes from low level to Hi-Z).
∗ For details, see "8.3. Fixed-cycle Interrupt Function". .
3) Time update interrupt function
The time update interrupt function generates interrupt events at one-second or one-minute intervals, according to the
timing of the internal clock.
When an interrupt event occurs, the UF bit value becomes "1" and the /INT pin goes to low level to indicate that an
event has occurred. (However, when a fixed-cycle timer interrupt event has been generated, low-level output from the
/INT pin occurs only when the value of the control register's UIE bit is "1". This /INT status is automatically cleared
(/INT status changes from low level to Hi-Z) 7.8 ms (a fixed value) after the interrupt occurs.
∗ For details, see "8.4. Time Update Interrupt Function".
4) Alarm interrupt function
The alarm interrupt generation function generates interrupt events for alarm settings such as date, day, hour, and
minute settings.
When an interrupt event occurs, the AF bit value is set to "1" and the /INT pin goes to low level to indicate that an
event has occurred.
∗ For details, see "8.5. Alarm Interrupt Function".
5) 32.768-kHz clock output
The 32.768-kHz clock (with precision equal to that of the built-in crystal oscillator) can be output via the FOUT pin.
The FOUT pin is a CMOS output pin which can be set for clock output when the FOE pin is at high level and for
low-level output when the FOE pin is at low level.
6) Interface with CPU
Data is read and written via the I
2
C bus interface using two signal lines: SCL (clock) and SDA (data).
Since neither SCL nor SDA includes a protective diode on the V
DD
side, a data interface between hosts with differing
supply voltages can still be implemented by adding pull-up resistors to the circuit board.
The SCL's maximum clock frequency is 400 kHz (when V
DD ≥
1.8 V), which supports the I
2
C bus's high-speed mode.
∗ For further description of data read/write operations, see "8.6 Reading/Writing Data via the I
2
C Bus Interface".