Bit banging

In computer engineering and electrical engineering, bit banging is a "term of art" for any method of data transmission that employs software as a substitute for dedicated hardware to generate transmitted signals or process received signals. Software directly sets and samples the states of GPIOs (e.g., pins on a microcontroller), and is responsible for meeting all timing requirements and protocol sequencing of the signals. In contrast to bit banging, dedicated hardware (e.g., UART, SPI, I2C) satisfies these requirements and, if necessary, provides a data buffer to relax software timing requirements. Bit banging can be implemented at very low cost, and is commonly used in some embedded systems. Bit banging allows a device to implement different protocols with minimal or no hardware changes. In some cases, bit banging is made feasible by newer, faster processors because more recent hardware operates much more quickly than hardware did when standard communications protocols were created. I2C bus protocol SPI bus - simultaneously transmit and receive a byte The following C language code example transmits a byte of data on an SPI bus. // transmit byte serially, MSB first void send_8bit_serial_data(unsigned char data) { int i; // select device (active low) output_low(SD_CS); // send bits 7..0 for (i = 0; i < 8; i++) { // consider leftmost bit // set line high if bit is 1, low if bit is 0 if (data & 0x80) output_high(SD_DI); else output_low(SD_DI); // pulse the clock state to indicate that bit value should be read output_low(SD_CLK); delay(); output_high(SD_CLK); // shift byte left so next bit will be leftmost data