用普单片机实现低成本高精度A_D与D_A转换关键词 单片机 　A/D转换 　D/A转换 　PWM(脉冲宽度调制)比较器-Pu realize low-cost single-chip microcomputer with high-precision conversion A_D with D_A Key words Single-chip A/D converter D/A converter PWM (pulse width modulation) comparator