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The purpose is to reduce the overall power demand compared to using both a strong pull-up and a strong pull-down. [10] A pure open-drain driver, by comparison, has no pull-up strength except for leakage current: all the pull-up action is on the external termination resistor.
In electronic logic circuits, a pull-up resistor (PU) or pull-down resistor (PD) is a resistor used to ensure a known state for a signal. [1] It is typically used in combination with components such as switches and transistors , which physically interrupt the connection of subsequent components to ground or to V CC .
A pull-up resistor (or pull-down resistor) can be used as a medium-impedance source to try to pull the wire to a high (or low) voltage level. If the node is not in a high-impedance state, extra current from the resistor will not significantly affect its voltage level.
At the physical layer, both SCL and SDA lines are an open-drain or open-collector bus design, thus a pull-up resistor is needed for each line. A logic "0" is output by pulling the line to ground, and a logic "1" is output by letting the line float (output high impedance) so that the pull-up resistor pulls it high. A line is never actively ...
Pull-up resistors are provided by the I3C controller. External pull-up resistors are no longer needed. Clock Stretching – devices are expected to be fast enough to operate at bus speed. The I3C controller is the sole clock source. I²C Extended (10-bit) Addresses. All devices on an I3C bus are addressed by a 7-bit address.
A logic high on the 1-Wire output, means the output of the FPGA is in tri-state mode and the 1-Wire device can pull the bus low. A low means the FPGA pulls down the bus. The 1-Wire input is the measured bus signal. On input sample time high, the FPGA samples the input for detecting the device response and receiving bits.
A common variation omits the collector resistor of the output transistor, making an open-collector output. This allows the designer to fabricate wired logic by connecting the open-collector outputs of several logic gates together and providing a single external pull-up resistor. If any of the logic gates becomes logic low (transistor conducting ...
Circuit designers will often use pull-up or pull-down resistors (usually within the range of 1–100 kΩ) to influence the circuit when the output is tri-stated. The PCI local bus provides pull-up resistors, but they would require several clock cycles to pull a signal high given the bus's large distributed capacitance .