最近买了块开发板学习单片机，以下是电路原理图。不明白上面的4×4矩阵键盘(电路图最左上角）的编码原理。键盘的8条引线直接与p1.0^p1.7相连，疑惑的是即使按下任意按键也在p1口上读不到任何电平啊？ 期待高手指点！-Recently bought a development board to study single-chip block, the following is the circuit schematic. Do not understand the above 4 × 4 m