What is the difference between a pull up and pull down?
Pull up is where you place a resistor between a signal and +V, pull down is pulling it to ground. Here, you can see that when the switch is open, in the pullup scenario the input pin will read high, but for pull down it will read low.
Similarly for input high, NMOS is ON, PMOS is OFF. The output is shorted to ground via NMOS. Hence we say, "output is pulled down to ground", hence the name pull down transistor for NMOS. Its withrespect to the output voltage level that we use the phrases "pull up"/"pull down"
- Bouncing is the tendency of any two metal contacts in an electronic device to generate multiple signals as the contacts close or open; debouncing is any kind of hardware device or software that ensures that only a single signal will be acted upon for a single opening or closing of a contact.
- I2C Pull Up Resistors. As discussed in the I2C Basics module, the resistors that are commonly seen on I2C circuits sitting between the SCL and SDA lines and the voltage source are called pull up resistors. A pull up resistor is used to provide a default state for a signal line or general purpose input/ouput (GPIO) pin.
- A MOSFET is known as a voltage controlled device because a voltage applied to the gate controls the flow of current between the source and drain. For a BJT the principal is the same. It is a current controlled device because the base current controls the current flow from the emitter to collector.
A pull-down resistor works in the same way but is connected to ground. It holds the logic signal near zero volts when no other active device is connected. The value of a pull down or pull up resistor will vary depending upon your specific devices involved.
- The positive end of a diode is called the anode, and the negative end is called the cathode. Current can flow from the anode end to the cathode, but not the other direction. If you forget which way current flows through a diode, try to remember the mnemonic ACID: “anode current in diode” (also anode cathode is diode).
- Voltage connected to the diode in this direction is called forward bias. But if you reverse the voltage direction, applying the positive side to the cathode and the negative side to the anode, current doesn't flow. In effect, the diode becomes an insulator.
- A device that blocks current in one direction while letting current flow in another direction is called a diode. Diodes can be used in a number of ways. For example, a device that uses batteries often contains a diode that protects the device if you insert the batteries backward.
Updated: 26th November 2019