The System Management Bus (abbreviated to SMBus or SMB) is a single-ended simple two-wire bus for the purpose of lightweight communication. It is derived from I²C for communication with low-bandwidth devices on a motherboard, especially power related chips such as a laptop's rechargeable battery subsystem; other devices might include temperature, fan or voltage sensors, lid switches and clock chips. PCI add-in cards may connect to an SMBus segment.
SMBus is almost completely compatible with I2C; the notable differences, including voltage, current and clock, can be found in the link below:
The SMBus standard is based on 2.1V, whereas UX2 is based on 3.3V. You will need to use a level shifter, or reduce the UX2 voltage directly.
UX2 doesn't provide direct support for SMBus, but as it's practically compatible with I2C any of the I2C pin variants could be used...
UX2-GPIO – 1 x I2C, 4 x GPIO, 1 x UART, 1 x SPI:
UX2-1IS – 1 x I2C, 1 x 1-WIRE, 1 x INTERRUPT, 1 x UART, 1 x SPI, 1 x SOUND-WIRE:
UX2-ALT – 2 x I2C, 2 x GPIO, 1 x UART, 1 x SPI:
UX2-I2C – 3 x I2C, 1 x UART, 1 x SPI:
The I2C standard uses 4 wires; SDA (data), SCL (clock), 3V3 and GND:
| UX2 | SMBus |
|---|---|
 |
SMBDAT (data) |
 |
SMBCLK (clock) |
 |
Incompatible, use 2.1V instead |
 |
GND |
Like I2C, SMBus can have several devices attached to it in a linear topology:
SMBus is designed for use within a circuit board, rather than remote sensing or inter-device comms; wire lengths should be kept short. If you need longer range, use I2C instead.
- UX2 Overview
- Protocols
- I2C – almost completely compatible with SMBus.
- Modules