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2. APPLICATION
MITSUBISHI MICROCOMPUTER
3819 Group
2.9 Clock generating circuit
3819 Group USER’S MANUAL
Power failure detection signal
Input port
(Note)
3819 group
Signal is detected by inputting
to each input port, interrupt
input pin, and analog input pin.
Note :
XIN
XCIN
Internal system
clock
f(XIN)/2
f(XCIN)/2
Change the internal
system clock to f(XIN)/2
(high-speed mode).
f(XIN)/8
Release reset
Detection of power failure
Selection of XCIN
oscillating function
After detecting a power
failure, change the internal
system clock to f(XCIN) and
stop operating of f(XIN).
(2) Counting without clock error during a power
failure
Outline : It keeps counting without clock errors
during a power failure.
Specifications :
Keep a power consumption as low as possible
while maintaining a clock function.
Keep counting a clock correctly.
f(XIN) = 4.19 MHz, f(XCIN) = 32.768 kHz
The Timer 1 interrupt is used in a normal power state.
The Timer 3 interrupt is used during a power failure.
Port processing
Input port : Fix to “H” or “L” level in the external
unit.
Output port : Fix to an output level which does not
cause a current flow to the external
unit.
[
Example]
When a circuit turns on LED at “L” output level, fix the output level to “H”.
I/O port : Input port — Fix to “H” or “L” level in the external unit.
Output port — Output the data which does not consume current.
VREF : Supplying to the Reference voltage input pin is stopped by the external circuit.
P45/ZCR (using as the input port) : Fix to “H” level in the external unit.
Figure 2.9.15 shows a timing chart of counting without clock errors during a power failure, Figure 2.9.16 shows a
structure of a clock counter, and Figures 2.9.17 and 2.9.18 show a setting of related registers.
Fig. 2.9.15 Timing chart of counting without clock errors during a power failure
Fig. 2.9.14 Connection diagram [Counting without
clock errors during a power failure]