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 tables summarize the differences between the two buses.


Clock Speed Comparison
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

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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