STC89C52RC 看其規格書里面介紹有上拉電阻:請看如下:
Port0 :Port0 is an 8-bit bi-directional I/O port with pull-up resistance.
Except being as GPIO, Port 0 is also the multiplexed low-order address
and data bus during accesses to external program and data memory.
STC89C52RC用過，STC其它系列也用過，都沒聽說過有上拉電阻！！！
Port0 :Port0 is an 8-bit bi-directional I/O port with pull-up resistance.這句話說的好象是有上拉電阻一樣，STC是國產的芯片，真沒看過英文手冊。你可以看一下IO口的內部示意圖，找一下設置或打開內拉電阻的寄存器來驗證。
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