20 STC12C5Axx
Technical Summary
Open-drain Output
The open-drain output configuration turns off all pull-ups and only drives the pull-down
transistor of the port pin when the port register contains logic “0”. To use this configuration in
application, a port pin must have an external pull-up, typically tied to VDD. The input path of
the port pin in this configuration is the same as quasi-bidirection mode.
Port pin
Input data
Port latch data
Input-only Mode
The input-only configuration is a Schmitt-triggered input without any pull-up resistors on the
pin.
Port pin
Input data
Push-pull Output
The push-pull output configuration has the same pull-down structure as both the open-drain
and the quasi-bidirectional output modes, but provides a continuous strong pull-up when the
port register contains a logic “1”. The push-pull mode may be used when more source current
is needed from a port output.
VDD
Port pin
Input data
Port latch data
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