Differences between I2C and SMBus

In general, the I2C bus and SMBus are compatible, but there are some subtle differences between the two that could cause some problems. The following table summarizes the differences between the two buses.

Clock Speed Comparison

	I2C	SMBus
Minimum	none	10 kHz
Maximum	100 kHz (Standard mode) 400 kHz (Fast mode) 2 MHz (High Speed mode)	100 kHz
Timeout	none	35 ms

Electrical Characteristics Comparison

	I2C	SMBus
VHIGH	Fixed Voltage: 3.0 to VDD_max + 0.5V VDD Relative: 0.7 to VDD_max + 0.5V	2.1V to VDD
VLOW	Fixed Voltage: -0.5V to 1.5V VDD Relative: -0.5 to 0.3VDD	to 0.8V
Max Current	3 mA	350 µA

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