Cautions For Power-On-Clear Circuit - NEC 78K0 Series User Manual

23.4 Cautions for Power-on-Clear Circuit

In a system where the supply voltage (V
voltage (V ), the system may be repeatedly reset and released from the reset status. In this case, the time from
POC
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
Setting 8-bit timer H1
(to measure 50 ms)
Note 1
No
50 ms has passed?
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.
534
CHAPTER 23 POWER-ON-CLEAR CIRCUIT
) fluctuates for a certain period in the vicinity of the POC detection
DD
Reset
Initialization
processing <1>
Power-on-clear
Clearing WDT
(TMIFH1 = 1?)
Yes
Initialization
processing <2>
Preliminary User's Manual U17260EJ3V1UD
Note 2
; Check the reset source
Initialize the port.
; f = Internal high-speed oscillation clock (8.4 MHz (MAX.)) (default)
PRS
Source: f (8.4 MHz (MAX.))/2
PRS
where comparison value = 102: ≅ 50 ms
Timer starts (TMHE1 = 1).
; Setting of division ratio of system clock,
such as setting of timer or A/D converter
12
,