4*4键盘扫描，采用列扫描法。依次对每列输出扫描电位，再从行输入扫描电平，通过该值判断被按下的键-4* 4 keyboard scanning, the use of column scanning method. Followed by scanning the output for each column potentials, input from the scan line level, the adoption of the value judgments of the key is pressed