关于IO口输入电流问题

清风***

在使用STC8G1K08单片机过程中，遇到一些问题，特来请教各位老师
先放上电路连接图


程序中P33口模式是准双向口，并将P33 = 0(后面不会改变此IO口的状态);使用外部中断检测IO电平变化，中断触发为上升沿和下降沿都中断。
当开关闭合时，MOS管导通，会产生一个上升沿，但是此时的电流达到46mA
查看IO口内部结构时，当我给IO输入0时，红线经过的MOS管G极就为1，MOS管导通，电流经过MOS管到GND，由于我P33引脚上没有接电阻，5V经过外部的P沟道MOS管直接进入P33口，随后通过红线的路径到GND，此时是不是可以理解为5V和GND短路了呢？如果是短路，为什么电流只有46mA？46mA是不是已经超过单片机IO所能耐受的最大电流了？

清风***

电路没有其它负载产生电流

kk***

该电路是短路状态，但IO灌电流典型值只有20mA

清风***

kksk 发表于 2023-7-12 10:49
该电路是短路状态，但IO灌电流典型值只有20mA

是不是我让P33=0的时候，IO口内部的MOS管导通了，然后我外部的MOS管导通之后，5V直接经过IO口进入内部MOS管那里到GND，形成短路了？

j***

When the switch is closed, the MOS tube is turned on, and a rising edge will be generated, but the current at this time reaches 46mA.
If it is a short circuit, why  is the current only 46mA?  Has 46mA exceeded the maximum current that the microcontroller IO can stand?

You are correct to think 46mA is excessive, normally such a circuit is avoided as 46mA is too high for simple button sense.
You do not want to fight the LOW driving N-FET.
The reason you measure ~46mA is seen on these CMOS curves (from toshiba data, but applicable to all CMOS parts )




The 8051 port is designed with light pullups, so if you want to sense a switch to GND as your circuit shows, just omit the diode, and PFET and connect switch directly to P33 (you can use a 1k series resistor for ESD protection, if it is a remote switch)
P33 will then read HI for open switch and LO for closed switch.
As above, the peak curent needed through the switch is ~270uA at Vin ~ 2.0V, and drops to < 50uA at Vin = 0V
There is an optional 4.1k resistor pullup via P3PU, which can increase the switch current to ~ 1.2mA

清风***

jmg 发表于 2023-7-13 08:01
You are correct to think 46mA is excessive, normally such a circuit is avoided as 46mA is too high  ...

Thank you! The problem has been resolved.I connected a resistor in series at P3.3 and configured this port as a high impedence input.interruption can detect edge changes.