CHAPTER 15 POWER-ON-CLEAR CIRCUIT
Preliminary User’s Manual U16898EJ1V0UD
246
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
Power-on clear
; The r
eset source (power-on clear, WDT, or LVI)
can be identified by the RESF register.
;
TMIFH1 = 1: Interrupt request is generated.
;
Initialization of ports, etc.
;
8-bit timer H1 can operate on the low-speed Ring-OSC clock.
Source: f
RL
(480 kHz (MAX.))/2
7
×
compare value 200 = 53 ms
(f
RL
: Low-speed Ring-OSC clock oscillation frequency)
No
Note 1
Reset
Check reset
source
Note 2
Yes
50 ms has passed?
(TMIFH1 = 1?)
Initialization
processing
Timer starts
(set to 50 ms)
Notes 1. If reset is generated again during this period, initialization processing is not started.
2. A flowchart is shown on the next page.
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