MB95630H Series
MN702-00009-2v0-E FUJITSU SEMICONDUCTOR LIMITED 511
CHAPTER 24 I
2
C BUS INTERFACE
24.6 Operations and Setting Procedure Example
24.6.2 Function to Wake up the MCU from Standby Mode
The wakeup function enables the I
2
C macro to be accessed while the MCU is in
stop or watch mode.
■ Function to Wake Up the MCU from Standby Mode
The I
2
C macro includes a function to wake up the MCU from standby mode. The function is
enabled by writing "1" to the IBCR0n:WUE bit.
With the MCU in stop mode or watch mode and the IBCR0n:WUE bit set to "1", if a start
condition is detected on the I
2
C bus, the wakeup interrupt request flag bit (IBCR0n:WUF) is
set to "1" and the wakeup interrupt request is generated to wake up the MCU from stop/watch
mode.
• Set IBCR0n:WUE to "1" immediately before setting the MCU to stop or watch mode.
Similarly, clear IBCR0n:WUE (by writing "0") after the MCU wakes up from stop or watch
mode so that I
2
C operation can restart as soon as possible.
• The wakeup function only applies to the MCU stop and watch modes.
Figure 24.6-7 Comparison of Normal I
2
C Operation and Wakeup Operation
SDAn
SCLn
IRQ by
IBCR0n:WUF
Machine
Clock
1
2
3 4
5
➀ Set the IBCR0n:WUE bit to "1" immediately before entering stop/watch mode and make sure that IBSRn:BB = 0.
➁ Set the MCU to stop/watch mode and the machine clock stops.
➂ Detect a start condition in stop mode or watch mode. IBCR0n:WUF is set to 1 and a wakeup IRQ is generated. In stop
mode, after the oscillation stabilization wait time, the MCU wakes up and enters the clock mode used before entering stop
mode or watch mode.
➃ Clear the IBCR0n:WUE bit to "0" so that I
2
C can restart the normal operation, and clear the IBCR0n:WUF bit to "0" to clear
the wakeup interrupt.
➄ To receive the data byte correctly, the SCLn must be released in the first cycle after 100 μs (assuming a minimum
oscillation stabilization wait time of 100 μs) from the start of I
2
C transmission (falling edge detection of SDAn).
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