STC89C52RC 看其规格书里面介绍有上拉电阻:请看如下:
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用过,STC其它系列也用过,都没听说过有上拉电阻!!!
Port0 :Port0 is an 8-bit bi-directional I/O port with pull-up resistance.这句话说的好象是有上拉电阻一样,STC是国产的芯片,真没看过英文手册。你可以看一下IO口的内部示意图,找一下设置或打开内拉电阻的寄存器来验证。