外面什么不接也不行？另外80脚的芯片要注意下先禁止EB， 见数据手册11.6PORTE, TRISE and LATE Registers
On 80-pin devices, PORTE is multiplexed with the system bus as part of the External Memory Interface. I/O port and other functions are only available when the interface is disabled by setting the EBDIS bit(MEMCON<7>).
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