一个四位二进制加/减运算器。 要求：当控制端G＝0时做加运算，G＝1时做减运算。用发光二极管表示运算结果的正、负。用数码管显示运算结果：加运算时，相加之和不超过15，减运算时，结果可正可负，但都用原码表示。-Plus a four binary/by calculator. Requirements: When the control terminal G = 0 when computing increases, G = 1 when computing reduced. Computin

基于VHDL的8-3优先编码器模块，din0-din7八位二进制输入编码后输出三位编码结果。采用正逻辑设计，高电平有效。-8-3 priority encoder module, based on VHDL din0- din7 eight binary input encoded output three coding results. Adopt positive logic design, high level effectively.