实验图1是一含计数使能、异步复位和计数值并行预置功能4位加法计数器，例1是其VHDL描述。由实验图1所示，图中间是4位锁存器；rst是异步清信号，高电平有效；clk是锁存信号；-Figure 1 is a test with count enable, asynchronous reset and preset features include numerical parallel adder four counters, Example 1 is described in VHDL. By experiment shown in Figure 1, Figure 4 is the intermediate latch　rst clearance signal is asynchronous, high effective　clk is a latch signal