Interface circuit composed of 8051 single chip microcomputer and 74LS165

The figure below shows the interface circuit between 8051 microcontroller and 74LS165. The serial port of 8051 microcontroller works in mode 0, which is synchronous shift register input/output mode. The data received/sent is 8 bits, with the low bit first, and there is no start bit, parity bit and stop bit.

Serial data is input from RXD (P3.0), and the shift clock is output from TXD (P3.1). Port line P1.7 is used to control the working state of 74LS165. When P1.7 outputs a low level, 74LS165 puts parallel data into the register; when P1.7 outputs a high level, 74LS165 works in a serial shift state under clock control, and data is shifted into the 8051 microcontroller through RXD (P3.0).