What is open drain mode in GPIO?
Open-drain output configuration is nothing but the top PMOS transistor is deactivated as shown in Figure1. When the transistor is ON, the pin pulled to the ground. When the transistor is OFF, the drain of the transistor will be floating or open. That’s the reason it is called an open drain.
What is the use of open drain on a GPIO output pin?
Open-drain outputs are useful when multiple gates or pins are connected together, such as with the I2C bus. When a device is not using the bus, the open-drain output is in high-impedance mode and the voltage level is pulled high by the pull-up resistor.
What is an open drain output?
An open-drain or open-collector output pin is driven by a single transistor, which pulls the pin to only one voltage (generally, to ground). When the output device is off, the pin is left floating (open, or hi-z).
What is the difference between push-pull and open drain output type?
While a push-pull sensor has two MOSFETs that alternately conduct to provide high or low output signals, an open drain sensor has only one MOSFET. When a magnetic field turns the open-drain sensor on, the MOSFET conducts, allowing current to sink through the pull-up resistor to ground.
What is the advantage of open drain output over push pull output?
Open drain output has higher power consumption during active transfers due to the pull-up resistors that are used. In general, the push-pull output has faster slopes than the open drain output.
What is open drain?
The term “open drain” means there’s a current sink, but on a FET device, for example, a MOSFET. (A MOSFET is like a transistor that can handle higher voltages but operates in much the same way.) The term “open collector” refers to a current sink on a transistor output.
What is open drainage?
An open drain is an open channel, mostly found in urbanized areas and used for the discharge of rainwater. Rainwater collected by the channels is often directed to rivers or other water sources. And when the rainy season begins, the open drains can rapidly spread water-borne diseases and infections.
What is the purpose of open drain?
Open-drain outputs can be useful for analog weighting, summing, and limiting as well as digital logic. An open drain terminal is connected to ground when a high voltage (logic 1) is applied to the gate, yet presents a high impedance when a low voltage (logic 0) is applied to the gate.
How does GPIO work in open drain configuration?
Open Drain GPIO 1 PMOS doesn’t exist in open-drain configuration and the output has two possibilities high or floating. 2 NMOS will get activated by giving 0 in the output data register and the I/O pin is to the ground. 3 Output data register will leave the port in Hi-Z when it is given and I/O state is not defined.
When to use the flags in GPIO descriptor?
The two last flags are used for use cases where open drain is mandatory, such as I2C: if the line is not already configured as open drain in the mappings (see GPIO Mappings ), then open drain will be enforced anyway and a warning will be printed that the board configuration needs to be updated to match the use case.
What happens to GPIO output when transistor is switched off?
The drain will get open when the transistor is switched off, so the output will float. Open-drain output configuration can’t pull up the pin it can only pull down the pin. The open-drain output configuration of GPIO is useless until and unless it is provided with pull up capability
How does the GPIO descriptor consumer interface work?
With the descriptor-based interface, GPIOs are identified with an opaque, non-forgeable handler that must be obtained through a call to one of the gpiod_get () functions. Like many other kernel subsystems, gpiod_get () takes the device that will use the GPIO and the function the requested GPIO is supposed to fulfill: