CHAPTER 15 POWER-ON-CLEAR CIRCUIT
User’s Manual U16898EJ3V0UD
247
15.4 Cautions for Power-on-Clear Circuit
In a system where the supply voltage (V
DD
) fluctuates for a certain period in the vicinity of the POC detection
voltage (V
POC
), the system may be repeatedly reset and released from the reset status. In this case, the time from
release of reset to the start of the operation of the microcontroller can be arbitrarily set by taking the following action.
<Action>
After releasing the reset signal, wait for the supply voltage fluctuation period of each system by means of a
software counter that uses a timer, and then initialize the ports.
Figure 15-3. Example of Software Processing After Release of Reset (1/2)
•
If supply voltage fluctuation is 50 ms or less in vicinity of POC detection voltage
; Check reset source
Note 2
Initialization of ports
Setting WDT
Source :
f
RL
(
2.1 MHz
(
MAX.
)) /
2
12
,
51 ms when the compare value is 25
Timer starts
(
TMHE1 = 1
)
Note 1
Setting 8-bit timer H1
(50 ms
is measured)
; S
pecify the division ratio of the system clock,
setting Timaer, setting
A/D Converter, etc.
Yes
No
; f
XP
= High-speed internal oscillation clock
(
8.4 MHz
(
MAX.
))
/2
2
(default value)
Reset
Initialization
processing <1>
Power-on clear
50 ms has passed?
(TMIFH1 = 1?)
Initialization
processing <2>
Clears WDT
Notes 1.
If reset is generated again during this period, initialization processing <2> is not started.
2.
A flowchart is shown on the next page.