说明：  AD7490驱动代码，verilog，采集电压是0~5v的电压采集，总共有十二个通道，每个通道轮训输出，欢迎采用该代码，谢谢，
(AD7490 driver code, verilog, the acquisition voltage is 0 ~ 5V voltage acquisition, a total of twelve channels, each channel output, welcome to use the code, thank you.)