I2C interfacing-II

 I2C or Inter-Integrated Circuit / Two-wire interface is a Multi-Master Serial protocol invented by Philips used to attach low-speed peripherals to a motherboard. It uses two open-drain bidirectional data lines SCL, SDL respectively.

  • The master is initially in master transmit mode by sending a start bit followed by the 7-bit address of the slave it wishes to communicate with, which is finally followed by a single bit representing whether it wishes to write(0) to or read(1) from the slave.
  • If the slave exists on the bus then it will respond with an ACK bit (active low for acknowledged) for that address. The master then continues in either transmit or receive mode (according to the read/write bit it sent), and the slave continues in its complementary mode (receive or transmit, respectively).
  • The address and the data bytes are sent most significant bit first. The start bit is indicated by a high-to-low transition of SDA with SCL high; the stop bit is indicated by a low-to-high transition of SDA with SCL high.
  • If the master wishes to write to the slave then it repeatedly sends a byte with the slave sending an ACK bit. (In this situation, the master is in master transmit mode and the slave is in slave receive mode.)
  • If the master wishes to read from the slave then it repeatedly receives a byte from the slave, the master sending an ACK bit after every byte but the last one. (In this situation, the master is in master receive mode and the slave is in slave transmit mode.)
  • The master then ends transmission with a stop bit, or it may send another START bit if it wishes to retain control of the bus for another transfer (a “combined message”).

I²C defines three basic types of messages, each of which begins with a START and ends with a STOP:

  • Single message where a master writes data to a slave;
  • Single message where a master reads data from a slave;
  • Combined messages, where a master issues at least two reads and/or writes to one or more slaves.

In a combined message, each read or write begins with a START and the slave address. After the first START, these are also called repeated START bits; repeated START bits are not preceded by STOP bits, which is how slaves know the next transfer is part of the same message.


Example:Interfacing AD5934

This chip is communicated by i2c protocol supported by some commands defined by the chip vendor.

To read and write to the registers of the IC the chip provide a list of interface commands

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Hello, I am Asim admin of this blog. An expert in Scientific Instrumentation (Analytical Instrumentation). My works are always associated with both Physics and electronics. Currently working on ARM based embedded systems for Optical(UV and Visible) and electrochemical spectroscopy (EIS). My M.Tech. Thesis was related to all these things. I had worked for a 8 bit microcontroller based standalone EIS (electrical impedance spectroscopy) device. I have Masters in Instrumentation engineering from NIT Kurukshetra,Haryana and Masters in Electronics Science from Sambalpur University, Odisha (Formerly Orissa/Utkal) Am also work for PHP MySQL AJAX based CMS design. i love blogging and coding(am not an expert).

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