W79E825A Datasheet, PDF (92/127 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E825A/824A/823B/822B Data Sheet
The “weak” pull-up is turned on when the input port pin is logic “1” level or itself is logic “1”, and it
provides the most source current for a quasi-bidirectional pin that output is “1” or port latch is logic “0”’.
The “very weak” pull-up is turned on when the port latch is logic “1”. If port latch is logic “0”, it will be
turned off. The very weak pull-up is support a very small current that will pull the pin high if it is left
floating. And the quasi-bidirectional port configuration is shown as below figure.
If port pin is low, it can drives large sink current for output, and it is similar with push-pull and open
drain on sink current output.
VDD
Port Latch
Data
2 CPU
Clock Delay
P _Strong P
Very
Weak
P _Weak
N
Port Pin
Input Data
Figure 20-2: Quasi-Bidirectional Output
20.2 Open Drain Output Configuration
To configure this mode is turned off all pull-ups. If used similar as a logic output, the port must has an
external pull-up resister. The open drain port configuration is shown as below.
Port Latch
N
Data
Port Pin
Input Data
Figure 20-3: Open Drain Output
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