97
3.6 Clocks
r Oscillation stabilization delay time at reset
The oscillation stabilization delay time at reset (the initial values of WT1 and WT0) is selected
as an option setting.
Products with power-on reset require an oscillation stabilization delay time when exit from stop
mode is triggered by resets in subclock mode (multiple), power-on reset, or external reset.
Products without power-on reset only require an oscillation stabilization delay time for watchdog
reset or software reset during subclock mode.
Table 3.6-3 "Main Clock Startup Conditions vs. Oscillation Stabilization Delay Time" shows the
relationships between the conditions in which main clock mode operation is started and
oscillation stabilization delay time.
s Subclock Oscillation Stabilization Delay Time
When an external interrupt returns the system from sub-stop (subclock oscillator stopped) to
sub-run mode (thus starting the subclock oscillator), a set subclock oscillation stabilization delay
time is provided. (This set delay time is equal to 215/FCL, where FCL is the subclock oscillator
frequency.)
The subclock oscillation stabilization delay time is also entered at power-on. Therefore, if you go
to subclock mode after power on, you should insert a software delay, to provide a longer delay
time before starting this transition than the subclock oscillation stabilization delay time alone.
The subclock oscillation stabilization delay time starts when the watch prescaler starts counting
up from the cleared state, and ends when it overflows.
Table 3.6-3 Main Clock Startup Conditions vs. Oscillation Stabilization Delay Time
Main clock mode
startup conditions
At power-on
During subclock mode
Exit from main-stop
Transition from
subclock to
main clock
mode (SYCC:
SCS*1=1)
External
reset
Software
reset and
watchdog
reset
External
reset
External
interrupt
Oscillation
stabilization delay
time selection
Option setting
SYCC: WT1, WT0 *2
With power-on
reset
O
OOO
O
No power-on reset
X
O
X
O
O:
Oscillation stabilization delay time provided
X:
Oscillation stabilization delay time not provided
*1
System clock select bit of system clock control register
*2
Oscillation stabilization delay time select bits of system clock control register