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 fr a me (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 fr a me data parallel output, LED1 showed that the data (sending timing as figure2shows). Then, use the software will TI reset, send the second fr a me data. The second fr a me data sending finished, LED1 shows the second fr a me data, the first fr a me data 74HC164 serial input to the second, LED2 shows the first fr a me data. By analogy, until the data in all data sending out. Should pay attention to, after all, data sent the first fr a me 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