Datasheet

29
AT89C51AC3
4383D–8051–02/08
Reset
Introduction The reset sources are : Power Management, Hardware Watchdog, PCA Watchdog and
Reset input.
Figure 16. 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
CC
as shown in Figure 17. Resistor
value and input characteristics are discussed in the Section “DC Characteristics” of the
AT89C51AC3 datasheet. The status of the Port pins during reset is detailed in Table 9.
Figure 17. Reset Circuitry and Power-On Reset
Power
Monitor
Hardware
Watchdog
PCA
Watchdog
RST
Internal Reset
RST
R
RST
VSS
To internal reset
RST
VDD
+
b. Power-on Reseta. RST input circuitry