Nations N32G45 Series, User Manual

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Nations Technologies Inc.
Tel
：
+86-755-86309900
Email
：
info@nationstech.com
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
22.3.6
SMBus
Introduction
The System Management Bus(SMBus or SMB) is a dual-wire bus interface. Using SMBus can communicate with
other device or other parts of the system, it able to commnicate with multiple devices without other independent
control wire. SMBus base on I2C commincate standard. SMBus have a control bus for system and power management
related tasks. If you want browse more information, please refer to the SMBus specification
V2.0(http://smbus.org/specs/).
SMBus have three types of device standard.

Master: device send command,generate clocks and stop transmmissions;

Slave: device receive,respond to commands;

Host: system have only one host. a device provides a master to system CPU. host have function of master and
slave, it support SMBus alert protocol.
SMBus is a subset of the data transmission format of the I2C specification.
Similarities between SMBus and I2C:

Both bus protocols contain of 2 wires (a clock wire SCL and a data wire SDA), with an optional SMBus alert
wire.

The data format is similar. SMBus data format is similar to 7-bit address format of I2C(See Figure 22-2).

Both are master-slave communication modes, and the master device provides the clock.

Both support multi master
Differences between SMBus and I2C:
Table 22-1 Comparison between SMBus and I2C
SMBus I
2
C
Maximum transmission speed 100kHz Maximum transmission speed 1MHz
Minimum transmission speed 10kHz No minimum transmission speed
Low clock timeout 35ms No clock timeout
Fixed logic level VDD determined logic level
Different address types (reserved, dynamic, etc.) 7-bit, 10-bit, and broadcast call slave address
types
Different bus protocols (quick command, call handling,
etc.)
No bus protocol
SMBus usage
SMBus uses the system management bus to meet lightweight communication requirements. In general, SMBus is
commonly used on the computer motherboard. It is mainly used to transmit ON/OFF instructions for power unit and
provide a control bus for system and power management-related tasks.
Device identification
On the SMBus, as a slave have a only address for any device, named slave address.