Shantanu Bhadoria > Device-SMBus-1.08 > Device::SMBus



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Module Version: 1.08   Source  


Device::SMBus - Control and read hardware devices with i2c(SMBus)


version 1.08


   use Device::SMBus;
   $dev = Device::SMBus->new(
     I2CBusDevicePath => '/dev/i2c-1',
     I2CDeviceAddress => 0x1e,
   print $dev->readByteData(0x20);


This is a perl interface to smbus interface using libi2c-dev library.


For Debian and derivative distros(including raspbian) use the following to install dependencies:

  sudo apt-get install libi2c-dev i2c-tools build-essential

If you are using Angstrom Linux use the following:

  opkg install i2c-tools
  opkg install i2c-tools-dev

For ArchLINUX use the following steps:

  pacman -S base-devel
  pacman -S i2c-tools

Special Instructions for enabling the I2C driver on a Raspberry Pi:

You will need to comment out the driver from the blacklist. currently the I2C driver isn't being loaded.

     sudo vim /etc/modprobe.d/raspi-blacklist.conf

Replace this line

     blacklist i2c-bcm2708

with this

     #blacklist i2c-bcm2708

You now need to edit the modules conf file.

     sudo vim /etc/modules

Add these two lines;


Now run this command(replace 1 with 0 for older model Pi)

     sudo i2cdetect -y 1

If that doesnt work on your system you may alternatively use this:

     sudo i2cdetect -r 1

you should now see the addresses of the i2c devices connected to your i2c bus



Device path of the I2C Device.

 * On Raspberry Pi Model A this would usually be /dev/i2c-0 if you are using the default pins.
 * On Raspberry Pi Model B this would usually be /dev/i2c-1 if you are using the default pins.


This is the Address of the device on the I2C bus, this is usually available in the device Datasheet.

 * for /dev/i2c-0 look at output of `sudo i2cdetect -y 0' 
 * for /dev/i2c-1 look at output of `sudo i2cdetect -y 1' 



returns IO::Handle->error() for the device handle since the last clearerr



This sends a single bit to the device, at the place of the Rd/Wr bit.



This reads a single byte from a device, without specifying a device register. Some devices are so simple that this interface is enough; for others, it is a shorthand if you want to read the same register as in the previous SMBus command



This operation is the reverse of readByte: it sends a single byte to a device.



This reads a single byte from a device, from a designated register. The register is specified through the Comm byte.



This writes a single byte to a device, to a designated register. The register is specified through the Comm byte. This is the opposite of the Read Byte operation.


 $self->readNBytes($lowest_byte_address, $number_of_bytes);

Read together N bytes of Data in linear register order. i.e. to read from 0x28,0x29,0x2a




This operation is very like Read Byte; again, data is read from a device, from a designated register that is specified through the Comm byte. But this time, the data is a complete word (16 bits).



This is the opposite of the Read Word operation. 16 bits of data is written to a device, to the designated register that is specified through the Comm byte.



This command selects a device register (through the Comm byte), sends 16 bits of data to it, and reads 16 bits of data in return.


 $self->writeBlockData($register_address, $values)

Writes a maximum of 32 bytes in a single block to the i2c device. The supplied $values should be an array ref containing the bytes to be written.

The register address should be one that is at the beginning of a contiguous block of registers of equal length to the array of values passed. Not adhering to this will almost certainly result in unexpected behaviour in the device.


 $self->readBlockData($register_address, $numBytes)

Read $numBytes form the given register address, data is returned as array

The register address is often 0x00 or the value your device expects

common usage with micro controllers that receive and send large amounts of data: they almost always needs a 'command' to be written to them then they send a response: e.g: 1) send 'command' with writeBlockData, or writeByteData, for example 'get last telegram' 2) read 'response' with readBlockData of size $numBytes, controller is sending the last telegram






I wrote this library for my Quadrotor project for controlling PWM Wave Generators ( ESC or DC motor controller ), Accelerometer, Gyroscope, Magnetometer, Altimeter, Temperature Sensor etc. However this module can also be used by anyone who wishes to read or control motherboard devices on I2C like laptop battery system, temperature or voltage sensors, fan controllers, lid switches, clock chips. Some PCI add in cards may connect to a 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 is used as an interconnect in several platform management standards including: ASF, DASH, IPMI.





Bugs / Feature Requests

Please report any bugs or feature requests through github at You will be notified automatically of any progress on your issue.

Source Code

This is open source software. The code repository is available for public review and contribution under the terms of the license.

  git clone git://


Shantanu Bhadoria <shantanu at cpan dott org>



This software is copyright (c) 2014 by Shantanu Bhadoria.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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