NT68P61A Datasheet, PDF (20/48 Pages) List of Unclassifed Manufacturers – 8-Bit Microcontroller for Monitor (24K OTP ROM Type)

NT68P61A
9. RESET
NT68P61A can be reset by the external reset pin or by
the internal watch-dog timer. This resets or starts the
microcontroller from a power-down condition. During the
time that this reset pin is held low (*reset line must be
held low for at least two CPU clock cycles), writing to or
from the µC is inhibited. When positive edge is detected
on the reset input, the µC will immediately begin reset
sequence.
After a system initialization time of six CPU clock cycles,
the mask interrupt flag will be set and the µC will load the
program counter from the memory vector locations
$FFFC and $FFFD. This is the start location for program
control. To improve noise immunity a Schmitt Trigger
buffer is provided at the RESET .
Reset status is as follows:
1. PORT0 PORT1. PORT2. PORT3 pins will act as
I/O ports with HIGH output.
2. Sync processor counters reset and VCNT | HCNT
latches cleared
3. All sync outputs are disabled
4. Base timer is disabled and cleared
5. A/D converter is disabled and stopped
6. DDC1/2B function is disabled
7. PWM DAC0 - DAC7 output 50% duty
waveform and DAC8 - DAC13 is disabled
8. Watch-dog timer is cleared and enabled
This RESET pin must be pulled high by external pulled-
up resistor (5KΩ suggestion), or it will stay low voltage to
reset system all the time.
10. Watch-dog timer (WDT) and Low Voltage
Reset Circuit (LVRC)
NT68P61A implements a watch-dog timer reset to avoid
system shut-down or malfunction. The clock of the WDT
is from on-chip RC oscillator not requiring any external
components. The WDT runs regardless if the clock of the
OSCI/OSCO pins of the device has been stopped. The
WDT time interval is about 0.5 second. The WDT must
be cleared within every 0.5 second when software is in
normal sequence, otherwise the WDT will overflow and
cause reset. The WDT is cleared and enabled after
system is reset. It cannot be disabled by software. Users
can clear the WDT by writing 55H to CLRWDT register.
NT68P61A will check voltage level of power supply.
When the voltage level of power supply is below a
threshold of 4.0V, the LVRC will issue a reset output to
the chip. After the power supply is restored to 4.0V and
above, the LVRC will keep reset signal low for 10mS and
then restore to high voltage. A power glitch of pulse
width less than 1µs will be ignored and no reset will
occur. This allows the µC enter the reset state in a good
condition. Refer to Figure 5 for the timing diagram.
as;
LDA #$55
STA $0012
Addr.
Register
INIT Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
$0012 CLR WDT
-
0
1
0
1
0
1
0
1
W
Vcc = 5.0 V
4.0 V
GND
System Reset
Hold 10 mS
Figure 5. LVR Reset Timing Diagram
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