How to read 8-bit I2C register using Arduino Wire library: A minimal example

The following code demonstrates how to read a register that is 1 byte (8 bits) long over I2C. It will work with almost all I2C devices like EEPROMs, ADCs and others, provided you have the correct. Note that some devices like the LAN9303 have a slightly different addressing scheme or other peculiarities. In my opinion, it’s most efficient to just try out the standard way of reading a register and start from there.

Note that this code does not implement error handling for the sake of simplicity. Additionally, we wait for data using delay() instead of Wire.available(). This is a minimal example so it creates minimal confusion for the reader. We will provide a full example with error handling in a followup post.

const uint8_t SLAVE_I2C_ADDRESS = 0b1010;
const uint16_t SLAVE_I2C_REGISTER_ADDRESS = 0x50;

Wire.beginTransmission(SLAVE_I2C_ADDRESS);
Wire.write(SLAVE_I2C_REGISTER_ADDRESS);
Wire.endTransmission();
Wire.requestFrom(SLAVE_I2C_ADDRESS, 1); // This register is 8 bits = 1 byte long
delay(2); // Wait for data to be available
// Read directly into an uint8_t
uint8_t buf = (uint8_t)Wire.read();
// Print register value
Serial.printf("Register value: %02x\r\n", buf);

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