Detailed explanation and selection of pull-up resistors and pull-down resistors

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Detailed explanation and selection of pull-up resistors and pull-down resistors [Copy link]

1. Definition 1. Pull-up means embedding an uncertain signal at a high level through a resistor! "The resistor also acts as a current limiter"! The same applies to pull-down! 2. Pull-up injects current into the device, while pull-down outputs current 3. Weak and strong are just different in the resistance value of the pull-up resistor, there is no strict distinction 4. For non-collector (or drain) open-circuit output circuits (such as ordinary gate circuits), the ability to increase current and voltage is limited. The function of the pull-up resistor is mainly to output current channels for open-collector output circuits. 2. Function of pull-up resistor 1. Generally, when used for single-key triggering, if the IC itself does not have an internal resistor, in order to keep the single key in an untriggered state or return to the original state after triggering, a resistor must be connected outside the IC. 2. There are three states of digital circuits: high level, low level, and high resistance state. In some applications, high resistance state is not desired. It can be stabilized by pull-up resistors or pull-down resistors, depending on the design requirements! 3. Generally speaking, I/O ports can be set, some cannot be set, some are built-in, and some need to be externally connected. The output of the I/O port is similar to the C of a transistor. When C is connected to the power supply through a resistor, the resistor becomes the C pull-up resistor. That is to say, if the port is normally at a high level; when C is connected to the ground through a resistor, the resistor is called a pull-down resistor, which makes the port usually at a low level. What is the function: For example: "When a port connected to a pull-up resistor is set to input state, its normal state is high level, which is used to detect low level input". 4. Pull-up resistors are used to provide current when the bus driving capability is insufficient. Generally speaking, it is pulling current, and pull-down resistors are used to absorb current, which is what we usually call current sinking 5. Connecting resistors is to prevent the input terminal from being left floating 6. Reduce the interference of external current on the chip 7. Protect the protection diode in CMOS, the current is generally not more than 10mA 8. Increase or decrease the driving current by pulling up or down 9. Change the potential of the level, commonly used in TTL-CMOS