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XC2200 Derivatives
System Units (Vol. 1 of 2)
System Control Unit (SCU)
User’s Manual
6-45
V2.1, 2008-08
SCU, V1.13
The wake-up interval counter (WIC) is clocked with
f
SYS
/64, and counts down until it
reaches zero. It then generates a wake-up trigger and sets bit WUCR.WUTRG.
The timer is stopped in the following ways:
•
bit WUCR.RUN is cleared
•
bit WUCR.ASP is set AND a wake-up trigger is generated
If the counter WIC is not stopped by its zero trigger it continues counting down from
FFFF
H
.
Determination of Wake-up Period
The actual frequency of the trimmed current controlled wake-up clock (OSC_WU) can
be measured prior to entering power-save mode in order to adjust the number of clock
cycles to be counted (value written to WIC), and such, to define the time until wake-up.
The period of OSC_WU can be measured by evaluating its (synchronized) clock output,
which can generate an interrupt request or which can be monitored via bit
WUCR.TTSTAT.
As using an interrupt together with software contain some uncertainty there is a second
way to determine the wake-up period. The wake-up triggers generated by the WUT are
forwarded to the CCU60 and can there be evaluated compared to the accurate system
clock.