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T0CS: TMR0 Clock Source Select bit
1 = Transition on T0CKI pin or CPSOSC signal [default]
0 = Internal instruction cycle clock (FOSC/4)

很奇怪的一選項,應該說是搞不懂預設值為何是1?
若不把這個T0CS設為0,則該PIN腳就無法當GPIO用了...