树莓派（Raspberry Pi）python smbus 函数说明

刚开始学习树莓派，在使用I2C接口时遇到了一些问题，比如不了解smbus有那些函数和这些函数的使用方法，网上找了很久也没有找到具体说明smbus函数的文档，现将我整理的一些说明资料归档如下，一方面便于自己后期学习，二方面便于刚接触树莓派，想要更深入学习I2C接口功能的朋友们，希望对大家有所帮助：

       使用方法：

首先在程序中导入“smbus”模块，方法如下：

#导入方法一：
import smbus

#导入方法二：
from smbus import SMBus

#创建一个smbus实例
b = smbus.SMBus(1)

b = SMBus(1)    # 0 代表 /dev/i2c-0， 1 代表 /dev/i2c-1
                #具体看使用的树莓派那个I2C来决定。

#实例创建好了就可以使用i2c函数了
b.read_byte_data(0x2f,0x58)

 

	function	description	parameters	return value
	SMBus Access
	write_quick (addr)	Quick transaction.	int addr	long
	read_byte (addr)	Read Byte transaction.	int addr	long
	write_byte (addr, val)	Write Byte transaction.	int addr, char val	long
	read_byte_data (addr, cmd)	Read Byte Data transaction.	int addr, char cmd	long
	write_byte_data (addr, cmd, val)	Write Byte Data transaction.	int addr, char cmd, char val	long
	read_word_data (addr, cmd)	Read Word Data transaction.	int addr, char cmd	long
	write_word_data (addr, cmd, val)	Write Word Data transaction.	int addr, char cmd, int val	long
	process_call (addr, cmd, val)	Process Call transaction.	int addr, char cmd, int val	long
	read_block_data (addr, cmd)	Read Block Data transaction.	int addr, char cmd	long [ ]
	write_block_data (addr, cmd, vals)	Write Block Data transaction.	int addr, char cmd, long [ ]	None
	block_process_call (addr, cmd, vals)	Block Process Call transaction.	int addr, char cmd, long [ ]	long [ ]
	I2C Access
	read_i2c_block_data (addr, cmd)	Block Read transaction.	int addr, char cmd	long [ ]
	write_i2c_block_data (addr, cmd, vals)	Block Write transaction.	int addr, char cmd, long [ ]	None

函数介绍：

Checking For Connected Devices

At the command prompt type one of these depending on whether you are using the I2C0 or I2C1 port: 

sudo i2cdetect -y 0
//or
sudo i2cdetect -y 1

The 7 bit I2C address of all found devices will be shown (ignoring the R/W bit, so I2C address 0000 0110 is displayed as hex 03).

SMBus (System Management Bus) is a subset from the I2C protocol
When writing a driver for an I2C device try to use the SMBus commands if possible (if the device uses only that subset of the I2C protocol) as it makes it possible to use the device driver on both SMBus adapters and I2C adapters.

Note address is the 7 bit address excluding the read / write bit (it will be shifted left 1 bit when added to the read/write bit)

# Send only the read / write bit 
long write_quick(int addr)

# Read a single byte from a device, without specifying a device register. 
long read_byte(int addr)

# Send a single byte to a device 
long write_byte(int addr, char val)

# Read Byte Data transaction. 
long read_byte_data(int addr, char cmd)

# Write Byte Data transaction. 
long write_byte_data(int addr, char cmd, char val)

# Read Word Data transaction. 
long read_word_data(int addr, char cmd)

# Write Word Data transaction. 
long write_word_data(int addr, char cmd, int val)

# Process Call transaction. 
long process_call(int addr, char cmd, int val)

#Read Block Data transaction.  
long[] read_block_data(int addr, char cmd)
    
# Write up to 32 bytes to a device.  This fucntion adds an initial byte indicating the 
# length of the vals array before the valls array.  Use write_i2c_block_data instead! 
write_block_data(int addr,char cmd,long vals[])

# Block Process Call transaction.  
long[] block_process_call(int addr, char cmd, long vals[])
 
   
# I2C Access Functions
# Block Read transaction. 
long[] read_i2c_block_data(int addr, char cmd)

#Block Write transaction. 
write_i2c_block_data(int addr, char cmd, long vals[])


#Code Example

#!/usr/bin/python

import smbus

bus = smbus.SMBus(1)    # 0 = /dev/i2c-0 (port I2C0), 1 = /dev/i2c-1 (port I2C1)

DEVICE_ADDRESS = 0x15      #7 bit address (will be left shifted to add the read write bit)
DEVICE_REG_MODE1 = 0x00
DEVICE_REG_LEDOUT0 = 0x1d

#Write a single register
bus.write_byte_data(DEVICE_ADDRESS, DEVICE_REG_MODE1, 0x80)

#Write an array of registers
ledout_values = [0xff, 0xff, 0xff, 0xff, 0xff, 0xff]
bus.write_i2c_block_data(DEVICE_ADDRESS, DEVICE_REG_LEDOUT0, ledout_values)