CHAPTER 23 POWER-ON-CLEAR CIRCUIT
Preliminary User’s Manual U17260EJ3V1UD
534
23.4 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 23-3. Example of Software Processing After Reset Release (1/2)
•
If supply voltage fluctuation is 50 ms or less in vicinity of POC detection voltage
;
Check the reset source
Note 2
Initialize the port.
Note 1
Reset
Initialization
processing <1>
50 ms has passed?
(TMIFH1 = 1?)
Initialization
processing <2>
Setting 8-bit timer H1
(to measure 50 ms)
; Setting of division ratio of system clock,
such as setting of timer or A/D converter
Yes
No
Power-on-clear
Clearing WDT
; f
PRS
= Internal high-speed oscillation clock (8.4 MHz (MAX.)) (default)
Source: f
PRS
(8.4 MHz (MAX.))/2
12
,
where comparison value = 102:
≅
50 ms
Timer starts (TMHE1 = 1).
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.