
31
AT89C51ID2
4289C–8051–11/05
Reset
Introduction
The reset sources are : Power Management, Hardware Watchdog, PCA Watchdog and
Reset input.
Figure 7. Reset schematic
Reset Input
The Reset input can be used to force a reset pulse longer than the internal reset con-
trolled by the Power Monitor. RST input has a pull-down resistor allowing power-on
reset by simply connecting an external capacitor to V
value and input characteristics are discussed in the Section “DC Characteristics” of the
AT89C51ID2 datasheet.
Figure 8. Reset Circuitry and Power-On Reset
Power
Monitor
Hardware
Watchdog
PCA
Watchdog
RST
Internal Reset
RST
R
RS
T
VSS
To internal reset
RST
VDD
+
b. Power-on Reset
a. RST input circuitry