8051 Microcontroller IO Port

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Alex1700

Joined Jan 12, 2020
15
What mean by quasi-bidirectional and true bidirectional IO ports in the 8051 microcontrollers?
What is the difference between these two type of io ports?
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DickCappels

Joined Aug 21, 2008
9,513
The definitions are included in the descriptions. True bidirectional port bits can be set to being imputed in which case they die a high impedance and are not internally driven (when set as outputs),

A quasi bidirectional port, when set to being an input,has a pull-up current source connected to it all the time it is used as an input.

In low power applications a quasi directional port will usually cause a higher current drain than the true bidirectional port. The trade-off is that the quasi bidirectional port does not need external pull-ups when reading switched to ground or open collector outputs,
 
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