BU9873 Datasheet, PDF (22/40 Pages) Rohm – I2C BUS Serial Interface RTC with High-precision Oscillation Adjustment

BU9873
Datasheet
6. Periodic Interrupt Function
The BU9873 can output periodic interrupt pulses in addition to alarm function from the INTRB pin. Output wave form for
periodic interrupt may be selected from regular pulse waveform (2Hz and 1Hz) and waveforms (every second, every minute,
every hour and every month) that are appropriate for CPU level interrupt. The condition of periodic interrupt signals can be
monitored with using a polling function.
6-1. Usage of Periodic Interrupt Function
Periodic interrupt function selection with setting value to register (internal address Eh)
CT2 CT1 CT0
0
0
0
0
0
1
Wave From
Mode
－
－
Description
Cycle and Falling Timing
OFF (Default)
Fixed at “L”
0
1
0 Pulse mode 2Hz (Duty50%)
0
1
1 Pulse mode 1Hz (Duty50%)
1
0
0 Level mode Every second (synchronized with second count-up)
1
0
1 Level mode Every minute (at 00 second of every minute)
1
1
0 Level mode Every hour (at 00 :00 of every hour)
1
1
1 Level mode Every month (1st day, 00:00:00 a.m. of every month)
Default
(1) Pulse mode：Outputs 2Hz, 1Hz clock pulses (duty 50%). Since counting up of second counter is delayed by
approximately 92μs from the falling edge of clock pulse, time reading immediately after the falling edge of clock pulse
may appear to lag behind the time counts of the real-time clocks by approximately 1 second.
CTFG bit
INTRB pins
Approx.92s（32.768kHz crystal is used）
(Counting up of seconds)
Figure 25. Output timing of pulse mode
(2) Level mode：One second, one minute or one month may be selected for an interrupt cycle. Counting up of seconds is
matched with falling edge of interrupt output. INTRB pin will be kept “L” until CTFG bit is set to “0”.
CTFG bit
INTRB pins
write 0 to CTFG
write 0 to CTFG
（Second count-up） （Second count-up） （Second count-up）
Figure 26. Output timing of level mode
(3) When the time trimming circuit is used, periodic interrupt cycle changes every 20 seconds.
Pulse mode: “L” duration of output of output pulses may change in the maximum rang of ±3.784ms.
For example, Duty will be 50±0.3784％at 1Hz.
Level mode: Frequency in one second may change in the maximum range of：±3.784ms.
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