AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 176

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

Reset Controlled by an
External Superviser Device
176
AT8xC5122/23
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
Superviser
device
Superviser
device
1N4148
1.8 K
RST
RST
Vcc
Vcc
10 K
10 K
To other on-board
circuitry
To other on-board
circuitry
Microcontrolleur
Microcontrolleur
Power Fail
Power Fail
Watchdog
Watchdog
Power On
Power On
Detector
Detector
Timer
Timer
Reset
Reset
4202D–SCR–06/05