CHAPTER 17 CLOCK MONITOR
Preliminary User’s Manual U16846EJ1V0UD
315
Figure 17-3. Timing of Clock Monitor (2/4)
(3) Clock monitor status after RESET input
(CLME = 1 is set after RESET input and at the end of high-speed system clock oscillation stabilization time)
CPU operation
Clock monitor status
CLME
RESET
Ring-OSC clock
High-speed
system clock
Reset
Oscillation stabilization time
Normal
operation
Clock supply
stopped
Normal operation (Ring-OSC clock)
Monitoring
Monitoring stopped
Monitoring
17 clocks
Set to 1 by software
RESET input clears bit 0 (CLME) of the clock monitor mode register (CLM) to 0 and stops the clock monitor
operation. When CLME is set to 1 by software at the end of the oscillation stabilization time (reset value of OSTS
register is 05H (2
16
/f
XP
)) of the high-speed system clock, monitoring is started.
Caution Waiting for the oscillation stabilization time is not required when the external RC oscillation
clock is selected as the high-speed system clock by the option byte. Therefore, the CPU clock
can be switched without reading the OSTC value. However, the clock monitor starts operation
after the oscillation stabilization time (OSTS register reset value = 05H (2
16
/f
XP
)) has elapsed.
(4) Clock monitor status after STOP mode is released
(CLME = 1 is set when CPU clock operates on high-speed system clock and before entering STOP mode)
Clock monitor status
Monitoring
Monitoring stopped
Monitoring
CLME
Ring-OSC clock
High-speed system
clock (CPU clock)
CPU operation
Normal
operation
STOP
Oscillation stabilization time
Normal operation
Oscillation
stopped
Oscillation stabilization time
(time set by OSTS register)
When bit 0 (CLME) of the clock monitor mode register (CLM) is set to 1 before entering STOP mode, monitoring
automatically starts at the end of the high-speed system clock oscillation stabilization time. Monitoring is stopped in
STOP mode and during the oscillation stabilization time.