Rainbow Electronics AT89C5122 - Manual (Page 176)

176
AT8xC5122/23
4202E–SCR–06/06
Reset Controlled by an
External Superviser Device As the reset pin can be forced in output by the Watch-Dog timer (WDT) or the POR/PFD
features, there can be a conflict between the external superviser device and the micro-
controller’s reset pin when in one side the external superviser is pulling the reset pin to
VCC and in another side the WDT or POR/PFD features tries to force the reset pin to
ground. Therefore, it recommended to insert a series resistor of 1.8K +/-10% or a diode
(1N4148 for instance) between the external superviser device and the reset pin as
detailed in the following figures.
Figure 106. Use of an External Serial Resistor
Figure 107. Use of an External Diode
RST
Vcc
10 K
Microcontrolleur
1.8 K
Superviser
device
To other on-board
circuitry
Power Fail
Detector
Watchdog
Timer
Power On
Reset
RST
Vcc
10 K
Microcontrolleur
Superviser
device
To other on-board
circuitry
Power Fail
Detector
Watchdog
Timer
Power On
Reset
1N4148