Talking about the March 8th Festival gift given by the girl

The pull-down resistor is directly connected to the ground. When the diode is connected, the end of the resistor is low level.

Because the lower bias resistor is connected to ground, it is called a pull-down resistor, which means to pull the level of the circuit node toward the low direction (ground). The main function of the pull-down resistor, together with the pull-up resistor, is to give the line (node) a fixed level when the circuit driver is turned off. 1. Increase the voltage level: a. When a TTL circuit drives a CMOS circuit, if the high level output by the TTL circuit is lower than the lowest high level of the CMOS circuit (usually 3.5V), then it is necessary to increase the voltage level at the output end of the TTL Connect a pull-up resistor to increase the value of the output high level.

b. A pull-up resistor must be added to the OC gate circuit to increase the high-level value of the output. 2. Increase the driving capability of the output pin. Pull-up resistors are often used on some microcontroller pins. 3. N/Apin anti-static and anti-interference: On CMOS chips, in order to prevent damage caused by static electricity, unused pins cannot be left floating. Generally, a pull-up resistor is connected to reduce the input impedance and provide a load discharge path. At the same time, if the pin is left floating, it is easier to accept electromagnetic interference from the outside. 4. Resistor matching to suppress reflected wave interference: Resistance mismatch in long-term transmission can easily cause reflected wave interference. Adding the pull-down resistor to resistor matching can effectively suppress reflected wave interference.