500
CHAPTER 24 STANDBY FUNCTION
User’s Manual U12697EJ3V0UM
Figure 24-12. Setting Timing for Subsystem Clock Operation
Main system clock
Subsystem clock
System clock
STBC
CST bit
Power supply
Stop main system clock oscillation.
00H
70H
74H
Subsystem clock
Main power supply
Backup power supply
Power supply switching
24.7.2 Returning to main system clock operation
When returning to main system clock operation from subsystem clock operation, the system power supply first
switches to the main power supply and enables the oscillation of the main system clock (set STBC = 70H). Then
the software waits the oscillation stabilization time of the main system clock, and the system clock switches to the
main system clock (set STBC to 00H).
Cautions 1. When returning from subsystem clock operation (stopped oscillation of the main system
clock) to main system clock operation, do not simultaneously specify bit MCK = 0 and bit
CK2 = 0 by write instructions to STBC.
2. The oscillation stabilization time specification register (OSTS) specifies the oscillation
stabilization time after the STOP mode is released, except when released by RESET, when
the system clock is the main system clock. This cannot be used when the system clock is
restored from the subsystem clock to the main system clock.
Figure 24-13 is the flow for restoring main system clock operation, and Figure 24-14 is the restore timing diagram.
