Glossary: high-impedance mode, pull-up Resistance

High-impedance Mode

High-impedance mode is a common term in a digital circuit. It refers to an output state of a circuit. It is neither high nor low. If a high-impedance state is input into a lower-level circuit, there is no impact on the lower-level circuit, and it is the same as not connected. If you use a multimeter for testing, it may be high or low, depending on what is next to it.

Essence of the high-impedance mode:

When the circuit is analyzed, the high blocking state can be understood as an open circuit. You can think of it as a very large output (input) resistor. His limit can be considered to be suspended. That is to say, in theory, the high-impedance state is not suspended. It is a State with great resistance to the ground or power supply. The actual application is almost the same as the pin suspension.

Typical applications:

1,In the structure of the bus connection. There are multiple devices mounted on the bus, and the devices are connected to the bus in the form of high resistance. In this way, the bus is automatically released when the device does not occupy the bus to facilitate other devices to obtain the right to use the bus.

2,Most single-chip I/O applications can be set to high-impedance input, such as lingyang and AVR. High-impedance input can be considered as infinite input resistance, and I/O has a very small impact on the front-level without generating current (no attenuation ), to some extent, it also increases the chip's ability to resist voltage impact.

Common representation of high-impedance states

The letter Z is commonly used in the high-impedance mode.

The pull-up and pull-up resistance is to embed uncertain signals at a high level through a resistor! The resistor can throttling at the same time! The same is true for the drop-down!
Pull-up refers to the injection of current to the device, and the drop-down refers to the output current. The weak strength is only the difference in the resistance of the pull-up resistor, so there is no strict distinction between them. For non-collector (or drain) open-circuit output circuits (such as common door circuits) provide limited capability to increase current and voltage. The pull-up resistance function is mainly used to output current channels of Open-collector output circuits. Why do we need to use the pull-up resistor?

Generally, when a single key is used for trigger, if the IC itself does not have an internal resistance, in order to make the single key remain in the not triggered status or return to the original status after the trigger, it must be connected to another Resistance Outside the IC.

There are three States for a digital circuit: high level, low level, and high resistance. In some applications, high resistance is not desired. In this case, you can use the pull-up or drop-down resistor to make it stable, depends on the design requirements!

Generally, I/O ports can be set, some cannot be set, some are built-in, and some need external connections. The output of I/O ports is similar to that of a transistor C, when C is connected to the power supply through a resistor, the resistor becomes the upper C resistor, that is, the port is high when it is normal; when C is connected to the ground through a resistor, the resistor is called a drop-down resistor.

The pull-up resistor is used to provide current when the bus drive capability is insufficient. The pull current is generally used to absorb the current.

Remarks: 51 Single-Chip Microcomputer P0 port is connected to the Pulling Resistance

I/O is pulled up and drop down, mainly to increase the stability of the controlled device when it is normal, it will not trigger the controlled device by mistake because the I/O voltage is unstable when the chip is started. In addition, it won't happen if you say that it is reduced from 1 to 0. When we pull it up and down, it will usually be a 10kb-level resistor. For example, you are connected to it, and I/O is normal. When you set the I/O port to low, the voltage of the pull-up resistor is divided into two ends, which will not cause the I/O port to be invalid. The principle is partial pressure. Let me show you a picture. It should be easy to understand.

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