Cannot output low level, why?


I use LM258 as avoltage comparator. When the output is low, it is sent to the MCU, but when the I/O port of the MCU is not connected, it can output the low level, but when the MCU is connected, it will no longer output low level. ,why? How to deal with it? I don’t have 339 and 393, so I can’t do it with them. I can’t help it. I know they can, I just tried it and it’s really fine.
Thanks in advance.


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