Datasheet

151
4337K–USB–04/08
AT89C5130A/31A-M
22. Reset
22.1 Introduction
The reset sources are: Power Management, Hardware Watchdog, PCA Watchdog and Reset
input.
Figure 22-1. Reset schematic
22.2 Reset Input
The Reset input can be used to force a reset pulse longer than the internal reset controlled by
the Power Monitor. RST input has a pull-up resistor allowing power-on reset by simply connect-
ing an external capacitor to V
SS
as shown in Figure 22-2. Resistor value and input
characteristics are discussed in the Section “DC Characteristics” of the AT89C5130A/31A-M
datasheet.
Figure 22-2. Reset Circuitry and Power-On Reset
22.3 Reset Output
As detailed in Section “Hardware Watchdog Timer”, page 158, the WDT generates a 96-clock
period pulse on the RST pin. In order to properly propagate this pulse to the rest of the applica-
tion in case of external capacitor or power-supply supervisor circuit, a 1 kΩ resistor must be
added as shown Figure 22-3.
Power
Monitor
Hardware
Watchdog
PCA
Watchdog
RST
Internal Reset
RST
RRST
VCC
To internal reset
RST
VSS
+
b. Power-on Reseta. RST input circuitry