'SMBUS'에 해당되는 글 1건

  1. 2009.01.14 SMBus 넌 머냐? - System Management Bus (2)
embeded/i2c2009. 1. 14. 16:08
SMBus는 예전에는 안보였는데, 어느샌가 부터 야곰야곰 보이기 시작한 녀석이다.
눈에 띄기 시작한건 아마도.. 2기가 급이 넘어 가면서 부터였던것 같다.(노트북 제외)

그냥 머하는건지 BUS인가 보다 넘어 갔는데 문득 호기심이 발동하였다.

I2C 처럼 BUS 방식의 시리얼 통신이고, 전원관리 칩들, 온도, 팬 , 전압 센서등 연결하고 있다고 한다.
예전 같으면 BIOS에서 cpu / chasis / system 온도계 3개만 지원했는데 비해서
요즘에는 센서들이 너무 많아서 일일이 하나의 GPIO를 할당하기에는 무리가 있어서 BUS로 돌렸나보다.

The System Management Bus (abbreviated to SMBus or SMB) is a simple two-wire bus, derived from I²C and used for communication with low-bandwidth devices on a motherboard, especially power related chips such as a laptop's rechargeable battery subsystem (see Smart Battery Data). Other devices might include temperature, fan or voltage sensors, lid switches and clock chips. PCI add-in cards may connect to an SMBus segment

The SMBus was defined by Intel in 1995. It carries clock, data, and instructions and is based on Philips' I²C serial bus protocol. Its clock frequency range is 10 kHz to 100 kHz. (PMBus extends this to 400 kHz.) Its voltage levels and timings are more strictly defined than those of I²C, but devices belonging to the two systems are often successfully mixed on the same bus.

[SMBus wikipedia : http://en.wikipedia.org/wiki/System_Management_Bus]

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

Electrical Characteristics
Fixed Voltage 3.0 to VDDmax + 0.5V
VDD Relative 0.7 to VDDmax + 0.5V
2.1V -> VDD
Fixed Voltage -0.5 to 1.5
VDD Relative -0.5 to 0.3VDD
to 0.8V
Max Current 3 mA 350 µA

[출처 : http://www.totalphase.com/support/articles/article06/]

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