两级轮询系统的FPGA实现，QuartusII9.0环境，VHDL语言，已编译仿真通过和指定管脚，可直接下载至板，不同板请重新制定-Two polling system FPGA, QuartusII9.0 environment, VHDL language, compiled through simulation and the specified pin can be directly downloaded to the board, please re-enact different b