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Why are pull-up resistors needed in open collector gates why not pull-down resistors?
Pull-up Resistor Summary A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.
Why does a pushbutton 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.
What does a 10K ohm resistor do?
What is a 10K ohm resistor? Commonly used in breadboards and perf boards, these 10K resistors make excellent pull-ups, pull-downs, and current limiters.
Do you need a resistor for Button?
Introduction: Arduino Button With No Resistor The resistor is mandatory for proper operation of a button, and everybody will insist on using it. However, there is a little secret embedded in each Arduino pin. Each pin already has a pull-up resistor that we can enable with just one small change in our code.
Why do you need a resistor before ground?
The resistor provides a path to ground for these stray electrons. To avoid grounding out the input, the resistance is set sufficiently high so that only a very small amount of the input current follows the path (current divider) to ground.
How are the pull up and pull down resistors connected?
By using these two pull-up resistors, one for each input, when switch “A” or “B” is open (OFF), the input is effectively connected to the +5V supply rail via the pull-up resistor.
What is the maximum pull up resistor for a logic gate?
By knowing the information above, we can calculate the maximum pull-up resistor value required for a single TTL 74LS series logic gate as: Then using Ohms Law, the maximum pull-up resistance required to drop 3 volts for a single TTL 74LS series logic gate would be 150kΩ.
How many pull up resistors are used in a NAND gate?
Two push buttons are used as an inputs to the AND gate. The pull-up resistor value is 10 kilo Ohm and the remaining components are 330 Ohm resistor and LED. The 330 Ohm resistor is connected in series to limit the current to the LED The circuit diagram of the NAND gate using 2-pull-down resistors at the i/ps to the NAND gate is shown below.
Can a TTL gate be connected to a pull up resistor?
Two or more open-collector outputs of TTL gates can be directly connected together and tied through a single external pull-up resistor. The result is that the outputs are effectively AND’ed together as the combination behaves as if the gates were connected to an AND gate. This type of configuration is called wired AND logic.