Wait
state
Start HIGH
period
I2Cx_SCL
from device #1
I2Cx_SCL
from device #2
Bus line
I2Cx_SCL
Architecture
992
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Inter-Integrated Circuit (I2C) Module
22.2.3 Clock Synchronization
Only one master device generates the clock signal (I2Cx_SCL) under normal conditions. However, there
are two or more masters during the arbitration procedure; and, you must synchronize the clock so that you
can compare the data output.
illustrates the clock synchronization. The wired-AND property of
I2Cx_SCL means that a device that first generates a low period on I2Cx_SCL (device #1) overrules the
other devices. At this high-to-low transition, the clock generators of the other devices are forced to start
their own low period. The I2Cx_SCL is held low by the device with the longest low period. The other
devices that finish their low periods must wait for I2Cx_SCL to be released before starting their high
periods. A synchronized signal on I2Cx_SCL is obtained, where the slowest device determines the length
of the low period and the fastest device determines the length of the high period.
If a device pulls down the clock line for a longer time, the result is that all clock generators must enter the
wait state. This way, a slave slows down a fast master and the slow device creates enough time to store a
received data word or to prepare a data word that you are going to transmit.
Figure 22-4. Synchronization of Two I2C Clock Generators During Arbitration
22.2.4 Signal Descriptions
The I2C peripheral has a serial data pin (I2Cx_SDA) and a serial clock pin (I2Cx_SCL) for data
communication, as shown in
. These two pins carry information between the device and other
devices that are connected to the I2C-bus. The I2Cx_SDA and I2Cx_SCL pins both are bi-directional.
They each must be connected to a positive supply voltage using a pull-up resistor. When the bus is free,
both pins are high. The driver of these two pins has an open-drain configuration to perform the required
wired-AND function.
See your device-specific data manual for additional timing and electrical specifications for these pins.
22.2.4.1 Input and Output Voltage Levels
The master device generates one clock pulse for each data bit that is transferred. Due to a variety of
different technology devices that can be connected to the I2C-bus, the levels of logic 0 (low) and logic 1
(high) are not fixed and depend on the associated power supply level. See your device-specific data
manual for more information.