CHAPTER 17 CLOCK MONITOR
Preliminary User’s Manual U16846EJ1V0UD
314
Figure 17-3. Timing of Clock Monitor (1/4)
(1) When internal reset is executed by oscillation stop of high-speed system clock
4 clocks of Ring-OSC clock
High-speed
system clock
Ring-OSC clock
Internal reset signal
CLME
CLMRF
(2) Clock monitor status after RESET input
(CLME = 1 is set after RESET input and during high-speed system clock oscillation stabilization time)
CPU operation
Clock monitor status
CLME
Ring-OSC clock
High-speed
system clock
Reset
Oscillation
stopped
Oscillation stabilization time
Normal
operation
Clock supply
stopped
Normal operation (Ring-OSC clock)
Monitoring
Monitoring stopped
Monitoring
Waiting for end
of oscillation
stabilization time
Oscillation
stopped
17 clocks
Set to 1 by software
RESET
RESET input clears bit 0 (CLME) of the clock monitor mode register (CLM) to 0 and stops the clock monitor
operation. Even if CLME is set to 1 by software during the oscillation stabilization time (reset value of OSTS register
is 05H (2
16
/f
XP
)) of the high-speed system clock, monitoring is not performed until the oscillation stabilization time of
the high-speed system clock ends. Monitoring is automatically started at the end of the oscillation stabilization time.
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.