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INA231

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SBOS644B – FEBRUARY 2013 – REVISED AUGUST 2017

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When the bus is idle, both the SDA and SCL lines are pulled high by the pull-up devices. The master generates

a start condition followed by a valid serial byte containing High-Speed (HS) master code 00001XXX. This

transmission is made in fast (400 kHz) or standard (100 kHz) (F/S) mode at no more than 400 kHz. The INA231

does not acknowledge the HS master code, but does recognize it and switches its internal filters to support 2.5-

MHz operation.

The master 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 2.5 MHz are allowed. Instead of using a stop condition, use repeated start conditions to secure the

bus in HS-mode. A stop condition ends the HS-mode and switches all the internal filters of the INA231 to support

the F/S mode. A bus timing diagram is shown in Figure 1.

8.5.6 SMBus Alert Response

The INA231 is designed to respond to the SMBus alert response address. The SMBus alert response provides a

quick fault identification for simple slave devices. When an alert occurs, the master can broadcast the alert

response slave address (0001 100) with the Read/Write bit set high. Following this alert response, any slave

devices that generated an alert identify themselves by acknowledging the alert response and sending their

respective address on the bus.

more than one slave attempts to respond, bus arbitration rules apply. The losing device does not generate an

acknowledge and continues to hold the ALERT line low until the interrupt is cleared.