Wire (I2C)

Slave mode (I2C)

This mode is generally used when you are connected to a different MCU that is the I2C master. For example, connecting to a Raspberry Pi using I2C where it is the I2C master.

I2C slave mode cannot be used at the same time as I2C master mode on the Particle device on the same pins; you generally will need to use a separate Wire interface on different physical pins if you need both.

One scenario where this can be confusing is when there are built-in I2C peripherals on the device. Some examples include:

Device Interface Purpose
B-SoM Wire (D0/D1) PMIC and Fuel Gauge on eval board
Boron Wire1 PMIC and Fuel Gauge
M-SoM Wire (D0/D1) PMIC and Fuel Gauge on eval board
Muon Wire (D0/D1) PMIC, Fuel Gauge, Temperature sensor, EEPROM
Monitor One Wire (A0/A1) Temperature Sensor, User LEDs
Monitor One Wire1 PMIC and Fuel Gauge
Tracker SoM Wire1 PMIC and Fuel Gauge

For example, if you are using the B-SoM on the evaluation board, you cannot use Wire (D0/D1) in I2C slave mode because the power manager is already using that interface in master mode if the power manager is enabled.

If you must use the same physical interface as the built-in PMIC and Fuel Gauge, you must disable the power manager using the following code:

void setup() {
    SystemPowerConfiguration conf;

Disabling the power manager will affect charge rates and input current limits, and may cause unpredictable behavior, especially with no battery connected.