当端口P0用作I / O端口时，输出低电平为0，输出高电平为高配置（不

When port P0 is used as an I/O port, the output low level is 0, and the output high level is high configuration (not 5V, equivalent to floating state). In other words, the P0 port cannot really output a high level and cannot provide current to the connected load, so a pull-up resistor (resistor connected to VCC) must be connected, and the power supply provides current to the load through the pull-up resistor. . Since port P0 does not have an internal pull-up resistor and is open-drain, no matter how great its drive capability is, it is equivalent to no power supply and needs to be provided by an external circuit. In most cases, a pull-up resistor must be added to port P0. <br>1. Generally, when P0 port of 51 single chip microcomputer is used as address/data multiplexing, it is not connected to the pull-up resistor. <br>2. When used as a general-purpose I/O port, since there is no internal pull-up resistor, a pull-up resistor must be connected. <br>3. When using port P0 to drive a PNP tube, no pull-up resistor is needed because the low level is valid at this time. 4. When using port P0 to drive the NPN tube, a pull-up resistor is needed, because at this time, only when P0 is 1, the back end can be turned on.

When port P0 is used as an I/O port, the output low is 0 and the output high is high (not 5V, equivalent to floating). That is, the P0 port does not really output a high level and does not provide current to the connected load, so a pull-up resistor (a resistor connected to the VCC) must be connected through which the power supply provides an up-current resistance to the load. Since port P0 does not have an internal pull-up resistor and is leaky and open, it is equivalent to no power supply, regardless of its drive capacity, and needs to be supplied by an external circuit. In most cases, the pull-up resistor must be added to port P0.<br>1. Typically, when the P0 port of a 51-chip machine is used as an address/data multiplent, it is not connected to the pull-up resistor.<br>2. When used as a universal I/O port, a pull-up resistor must be connected because there is no internal pull-up resistor.<br>3. When using port P0 to drive the PNP tube, there is no need to pull up the resistor, because the low level is valid at this time. 4. When using port P0 to drive the NPN tube, a pull-up resistor is required, as the back end can only be switched on if P0 is 1.

When port P0 is used as I / O port, the output low level is 0 and the output high level is high configuration (not 5V, equivalent to floating state). That is to say, the P0 port can not really output high level and can not supply current to the connected load, so a pull-up resistor (the resistor connected to VCC) must be connected, and the power supply supplies current to the load through the pull-up resistor. Because port P0 has no internal pull-up resistance and open drain, no matter how large its driving capacity is, it is equivalent to no power supply and needs to be provided by an external circuit. In most cases, the pull-up resistor must be added to port P0.<br>1. Generally, when the port P0 of 51 single chip microcomputer is used as address / data multiplexing, it is not connected to the pull-up resistor.<br>2. When used as a general-purpose I / O port, a pull-up resistor must be connected because there is no internal pull-up resistor.<br>3. When port P0 is used to drive PNP, pull-up resistor is not needed, because the low level is valid. 4. When using port P0 to drive NPN, a pull-up resistor is needed, because only when P0 is 1 can the back end be on.