I2C can be used to connect up to 127 nodes via a bus that only requires two data wires, known as
- SDA => D2.
- SCL => D1
SPI is much simpler than I2C. Master and slave are linked by three data wires, usually called MISO, (Master in, Slave out), MOSI (Master out, Slave in) and M-CLK.
- M-CLK => D5
- MISO => D6
- MOSI => D7
(SPI Bus SS (CS)is D8.)
Pin Function ESP-8266 Pin TX TXD TXD RX RXD RXD A0 Analog input, max 3.3V input A0 D0 IO GPIO16 D1 IO, SCL GPIO5 D2 IO, SDA GPIO4 D3 IO, 10k Pull-up GPIO0 D4 IO, 10k Pull-up, BUILTIN_LED GPIO2 D5 IO, SCK GPIO14 D6 IO, MISO GPIO12 D7 IO, MOSI GPIO13 D8 IO, 10k Pull-down, SS GPIO15 G Ground GND 5V 5V - 3V3 3.3V 3.3V RST Reset RST