ESP8266 - Testing the SPI interface using NodeMCU and Arduino Uno

This post is about how to test the SPI interface of ESP8266.

NodeMCU based ESP8266 has Hardware SPI with four pins (D5 ~ D8 in the red square below) available for SPI communication. With this SPI interface, we can connect any SPI enabled device with NodeMCU and make communication possible with it.

ESP8266 has SPI pins (SD1, CMD, SD0, CLK) which are exclusively used for Quad-SPI communication with flash memory on ESP-12E, hence, they can’t be used for SPI applications (the pins in the blue square). We can use Hardware SPI interface for user end applications.

Below figure shows Quad SPI interface pins that are internally used for flash. It consists quad i/o (4-bit data bus) i.e. four (SDIO_DATA0 – SDIO_DATA3) bidirectional (i/p and o/p) data signals with synchronize clock (SDIO_CLK) and chip select pin (SDIO_CMD). It is mostly used to get more bandwidth/throughput than dual i/o (2-bit data bus) interface.