控制移位寄存器的扩展

移位寄存器扩展用一个串入并出和并入串出寄存器链来扩展单片机的I/O功能，这个链共享时钟线和选通线，并且单片机有数据引脚来从链读取和输出数据-Control of extension shift register

The extension shift register extends the I/O capability of the micro by

using a chain of serial-parallel (for outputs) and parallel-serial (for

inputs) shift registers. The chain shares the same clock and strobe line,

and the micro has data pin that can be set to input or output to send or

receive data to/from the chain.