说明：  A/D模拟数字转换模块采用的是MX7821芯片，该芯片为双列直插20脚封装，管脚定义如图1所示。具体可以参考MX7821数据手册。MX7821读数据时序如图2所示。注意：MX7821最高工作频率为1MHz，也就是读信号RD周期不要小于1us。通信系统大型实验板上的MX7821没有外围芯片，有一个INPUT输入接口，输出8位数据线直接与FPGA相连。一个简单的数据采集程序MX7821.v
(A/D digital conversion module is MX7821 chips, the chip 20-pin DIP package, pin definitions shown in Figure 1. Specifically refer MX7821 Data Sheet. MX7821 read data series shown in Figure 2. Note: MX7821 maximum operating frequency of 1MHz, which is read signal RD cycle not less than 1us. Communication system is not large-scale experiment board MX7821 peripheral chips, there is a INPUT input interface, output 8-bit data lines connected directly with the FPGA. A simple data acquisition program MX7821.v)