This document introduces the implementation method of software SPI master communication and provides a hardware implementation scheme based on ST72251.
The document describes the principles of software-based SPI communication, defining the three required signal lines (CLK, MO, MI) and explaining how phase and polarity affect timing. It details the hardware configuration for a test setup involving an ST72251 microcontroller running at 8 MHz, where specific I/O ports are used to simulate full-duplex data transfer.
The driver performs a transmission of an 8-byte ROM buffer concurrently received on the MI line and stored in an 8-byte RAM buffer.
The maximum communication speed is 238.8 kHz, calculated based on the number of instruction cycles needed for the communication.