在做项目（工程）的时候，我们经常要用到比较多的按键，而且IO 资源紧张， 于是我们就想方设法地在别的模块中节省IO 口，好不容易挤出一两个IO 口，却...

代码说明：

在做项目（工程）的时候，我们经常要用到比较多的按键，而且IO 资源紧张， 于是我们就想方设法地在别的模块中节省IO 口，好不容易挤出一两个IO 口，却 发现仍然不够用，实在没办法了就添加一个IC 来扫键。一个IC 虽然价格不高， 但对于大批量生产而且产品利润低的厂家来说，这是一笔不菲的开支! 那，我们能不能想到比较好的扫键方法：用最少的IO 口，扫最多的键？可以吗？-Doing the project (engineering), we often use the relatively large number of keys, and the IO resource constraints, so we are trying to save in another module IO ports, finally out of one or two IO ports, only to find is still not enough there is really no other way to add an IC to sweep on the keys. Although the price of an IC is not high, but low profits, high-volume production and product manufacturers, this is spending a lot of money! That, we can not think of a better scan key method: with a minimum of IO ports, scan Most of the keys? OK?