SPI Half-Duplex Example

This is an example of using SPI on ESP32 in half-duplex mode to transfer data between an ESP32-S3 (master) and ESP32-C6 (slave). It is based on the ESP-IDF SPI Half-Duplex Example.

This is intended to be a reference for implementing transfers using QSPI.

GPIO Configuration

For SPI

For SPI, the following values should be set in spi_bus_config_t:

• sclk_io_num (SCLK)
• mosi_io_num (MOSI)
• miso_io_num (MISO)

For QSPI

For QSPI, the following values should be set in spi_bus_config_t:

• sclk_io_num (SCLK)
• data0_io_num (DAT0)
• data1_io_num (DAT1)
• data2_io_num (DAT2)
• data3_io_num (DAT3)

GPIO Mappings between SPI and QSPI

Based on the structure of spi_bus_config_t found in spi_common.h:

• mosi_io_num is data0_io_num
• miso_io_num is data1_io_num
• quadwp_io_num is data2_io_num
• quadhd_io_num is data3_io_num

QSPI GPIOs for MCUs

Signal	ESP32-S3 (SPI2)	ESP32-C6 (SPI2)
CS	10	10
CLK	12	6
DAT0	11	7
DAT1	13	2
DAT2	14	5
DAT3	9	4

References

• ESP SPI Slave HD (Half Duplex) Mode Protocol
• ESP-IDF Issue (Closed) about using the example in QSPI mode
• ESP-IDF Issue (Closed) about using QPI mode
• SPI Slave Half Duplex documentation and API