When the bus is idle, both the SDA and SCL lines are pulled high by the pullup devices. The controller generates a start condition followed by a valid serial byte containing High-Speed (HS) controller code 00001XXX. This transmission is made in fast (400 kHz) or standard (100 kHz) (F/S) mode at no more than 400 kHz. The INA230 does not acknowledge the HS controller code, but does recognize it and switches its internal filters to support 3.4-MHz operation.

The controller then generates a repeated start condition (a repeated start condition has the same timing as the start condition). After this repeated start condition, the protocol is the same as F/S mode, except that transmission speeds up to 3.4 MHz are allowed. Instead of using a stop condition, repeated start conditions should be used to secure the bus in HS-mode. A stop condition ends the HS mode and switches all the internal filters of the INA230 to support the F/S mode.