利用AT89S51单片机的P1.0－P1.3接四个发光二极管L1－L4，用来指示当前计数的数据；用P1.4－P1.7作为预置数据的输入端，接四个拨动开关K1－K4，用P3.6/WR和P3.7/RD端口接两个轻触开关，用来作加计数和减计数开关。(The use of single-chip AT89S51 P1.0 P1.3 with four light emitting diode L1 L4, used to indicate the current count data; using P1.4 P1.7 as the input end of the preset data K1 K4 switch, four toggle, two touch switch with P3.6/WR and P3.7/RD port, used to count and count down switch.)