About MCU Pull-up Resistors-EEWORLD

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Since the P0 port has no pull-up resistor inside and is open-drain, no matter how strong its driving capability is, it is equivalent to having no power supply and needs an external circuit to provide it. In most cases, a pull-up resistor must be added to the P0 port.
1. Generally, the P0 port of the 51 single-chip microcomputer does not connect a pull-up resistor when used as address/data multiplexing.
2. When used as a general I/O port, since there is no pull-up resistor inside, a pull-up resistor must be connected! !
3. When the P0 port is used to drive the PNP tube, a pull-up resistor is not required because the low level is valid at this time;
4. When the P0 port is used to drive the NPN tube, a pull-up resistor is required because only when P0 is 1 can the rear end be turned on.
To put it simply, it must have a power supply to drive the LCD display, otherwise it will not light up. It happens that the P0 port has no power supply, so an external power supply must be connected. Connecting a resistor plays a role in current limiting; if it is connected to the P1, P2, and P3 ports, no external power supply and resistor are required.

The output port of some microcontrollers is open-collector! It can only provide two states: high-impedance and low level. In order to obtain high and low levels, a pull-up must be provided. At this time, the output port is like a switch to the ground. If the output is high level, the switch is open, and the output state is high level. If the output is low level, the switch is closed, and the output and the ground are short-circuited, forming a low level.

Keywords：MCU Reference address：About MCU Pull-up Resistors

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