有效，即允许RXD发送数据，同时，允许从TXD端输出移位脉冲。第一帧（8位）数据发送完毕时，各控制信号均恢复原状态，只有TI保持高电平，呈中断申请状态。第一个74HC164把第一帧数据并行输出，LED1显示该数据（发送时序如图2所示）。然后，用软件将TI清零，发送第二帧数据。第二帧数据发送完毕，LED1显示第二帧数据，第一帧数据串行输入给第二个74HC164，LED2显示第一帧数据。依此类推，直到把数据区内所有数据发送出去。应该注意，数据全部发送完后，第一帧数据在最后一个LED显示。由于TXD端最多可以驱动8个TTL门，当LED显示器超过8个时，我们采用74HC244芯片驱动。每个74HC244有8路驱动，每一路可驱动8个LED，即每增加一个74HC244，可增加64个LED驱动。

为了节省管脚，想用74164来做数码管。第一次做串行的东西。上了电以后，显示根本不对啊，测164并行输出口的高低电平，也是不对的。

-Effective, that allowed RXD send data, meanwhile, is allowed from TXD at output shift pulse. The first frame (8) data sending finished, the control signal are restored the original state, only keep a high level, TI application state interruption. The first 74HC164 put the first frame data parallel output, LED1 showed that the data (sending timing as figure2shows). Then, use the software will TI reset, send the second frame data. The second frame data sending finished, LED1 shows the second frame data, the first frame data 74HC164 serial input to the second, LED2 shows the first frame data. By analogy, until the data in all data sending out. Should pay attention to, after all, data sent the first frame data on the final LED display. Because most TXD end can drive eight TTL door when more than 8 LED display, we adopt 74HC244 chip driver. Each 74HC244 eight road drive, every way can drive eight LED, namely every add a 74HC244, can increase the 64 LED drivers.



In order to save the tube