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What do open drain outputs do in a circuit?
Open drain outputs act like a switch to ground. The resistor acts as a pullup for when none of the outputs are active. If you replace the open drain outputs in your circuit with buttons its easier to visualise: Thanks for contributing an answer to Electrical Engineering Stack Exchange!
What happens when the drain terminal is open?
If its drain terminal is open (the device is off) the pin is left floating to Hi-Z state. Driving it to high logic level requires the use of an additional circuit or component. In most cases, an external pull-up resistor is used (there are microcontrollers that provide internal pull-up resistors for open drain configurations).
Can a pull up resistor be used with an open drain?
There are few things that have to be considered when using a pull-up resistor with the open drain output configuration: Rising edge slope – The pull-up resistor in combination with the inherent capacitance of the line forms a low-pass filter.
What’s the difference between open drain and push pull?
Open Drain. In open drain configuration, the logic behind the pin can drive it only to ground (logic 0). The other possible state is high impedance (Hi-Z). The implementation involves the use of a single transistor. If its drain terminal is open (the device is off) the pin is left floating to Hi-Z state.
How does a pull up resistor work in a logic gate?
With a pull-up resistor connected, the output still works in the same way as a normal logic gate in that when the output transistor is OFF (open), the output is HIGH, and when the transistor is ON (closed), the output is LOW. Thus the transistor turns ON to pull the output to a LOW level.
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.
How is a pull up resistor connected to a Vcc supply?
This condition means that their output is either grounded when LOW, or floating when HIGH, so an external pull-up resistor, (Rp) needs to be connected from the open-collector terminal of the pull-down transistor to the Vcc supply.