Does UART need pull-up resistor?

A pull-up resistor on the UART serial Receive Data (RXD) input pin is not necessary because the RS232 line receiver is always driving that pin.

Which port needs external pull up resistors?

An external pull-up resistor is needed when Port 0 is defined as an output port. Port 0 of the 8051 has two main functions: To be used as a simple input-output port and to access external memory in conjunction with Port 2.

Are pull up resistors necessary?

Pull-up resistors are used to solve the dilemma for the microcontroller by pulling the value to a logical high state, as seen in the follow figure. Without the pull-up resistor, the MCU’s input would be floating when the switch is open and pulled down to a logical low only when the switch is closed.

Is UART open drain?

Push-pull output is best suited for communication interfaces that have single direction lines (e.g SPI, UART etc.). Open drain is commonly used for bidirectional single line communication interfaces, where more than two devices are connected on the same line(e.g I2C, One-Wire etc.)

Which out of the four ports of 8051 needs external pull up resistor for using it is as an input or an output port?

Discussion Forum

What is the purpose of a pull-up resistor?

Pull-up resistors are fixed value resistors used between the connection of a voltage supply and a particular pin in a digital logic circuit. More commonly paired with switches, its purpose is to ensure the voltage between Ground and Vcc is actively controlled when the switch is open.

Why does a button need a resistor?

The value of the pull-up resistor needs to be chosen to satisfy two conditions: When the button is pressed, the input pin is pulled low. The value of resistor R1 controls how much current you want to flow from VCC, through the button, and then to ground. When the button is not pressed, the input pin is pulled high.