Datasheet

7
7764A–8051–11/07
b) Using an external Brown-out device
Read application note “External Brown-out Protection for C51 microcontrollers with Active High
Reset Input“ (doc 4183).
Sometimes the RST pin may be internally forced by the WDT so that the external peripherals if
any are reset at the same time as the MCU. While the WDT is active the RST pin operates as an
output. Therefore the RST pin cannot be externally forced to a permanent level. If the external
Brown-out device operates in this way, an intermediate resistor Rint or a diode must be imple-
mented between the Brown-out device and the RST pin.
Brown-out device with an intermediate resistor
Brown-out device with a diode
RST
Internal Reset
Microcontroller
R
Brown-out
device
To other on-board
circuitry
Watchdog
Timer
Rint
VCC
RST
Internal Reset
Microcontroller
R
Brown-out
device
To other on-board
circuitry
Watchdog
Timer
1N4148
VCC