Try somthing like this (assuming button pressed = 0V, button released = 5V):
Button_Loop:
MOV A, P1
JNB ACC.0, NextButton
JNB ACC.1, BackButton
JNB ACC.2, AutoButton
JB AutoBut, AutoButton
MOV B, #10h
DJNZ B, $
SJMP Button_Loop
NextButton: ; display next character
CLR AutoBut
code .....
LJMP Button_Loop
BackButton: ; display previous character
CLR AutoBut
code .....
LJMP Button_Loop
AutoButton: ; auto display
SETB AutoBut
code .....
SJMP Button_Loop
Regards,
IanP