STC micro STC8A8K64D4 Series - Make I;O Port Output Low When Power on Reset

STC8A8K64D4 Series Manual
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- 177 -
I/O Pin
10K
2K
5V
5V
device
I/O Pin
9.8 Make I/O Port Output Low When Power on Reset
The general I/O port which is a weak pull-up (quasi-bidirectional) port will output high level when the traditional 8051
microcontroller is powered on and reset. Many practical applications require that certain I/O ports be low level output when powered
on, otherwise the system (such as the motor) controlled by the microcontroller will malfunction. The new generation of
STC8A8K64D4 series and STC8H series microcontrollers are high-impedance inputs after all I/O resets (except for P3.0/P3.1 which
are traditional weak pull-ups), adding a pull-down resistor can ensure low power when powered on If you want to change to high
level later, you only need to change the mode of I/O to strong push-pull output and output high level to the outside.
Now you can connect a pull-down resistor (about 10K) to the I/O port of STC microcontroller. In this way, during power-on
reset, except the download ports P3.0 and P3.1 are weak pull-ups (quasi-bidirectional ports), other I/O ports are in high-impedance
input mode, and there are external pull-down resistors, so this I/O When the port is powered on reset, the external level is low. If
you want to drive this I/O port to a high level, you can set this I/O port as a strong push-pull output, and when it is a strong push-
pull output, the driving current of the I/O port can reach 20mA, so you can definitely use this The port is driven as a high -level
output.
I/O Pin
Greater than 470
10K
This resistor is optional