通过PA口接8个开关K1～K8，开关向上为输入高电平，即逻辑‘1’。向下为输入低电平，即逻辑‘0’。PB口通过74LS240（8路，反相）接8个发光二极管的阴极，PB口输出‘1’，经74LS240反相输出‘0’，驱动发光二极管发光（参看实验一，图1• 1）。

从PA口读入8位开关的状态送PB口显示，拨动K1～K8，PB口上接的8个发光二极管L0～L7对应显示K1～K8的状态。

-I pick through the PA 8 switch K1 ~ K8, switch up the input high, the logic ' 1 ' . Down input low, that the logical ' 0 ' . PB export through 74LS240 (8 Lu, RP) received eight LED cathode, PB port output ' 1 ' , by 74LS240 inverting output ' 0' , drive light emitting diodes (see experiment 1, Figure 1 •　1). PA I read from the 8-bit switch state to send PB I showed Slide K1 ~ K8, PB 8 port on the connected light-emitting diode display the corresponding L0 ~ L7 K1 ~ K8 state.