1
0
0
0
1
0
0
0
1
1
1
1
1
0
Device #1 lost arbitration
and switches off
Bus line
I2Cx_SCL
Data from
device #1
Data from
device #2
Bus line
I2Cx_SDA
Architecture
998
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Inter-Integrated Circuit (I2C) Module
22.2.9 Arbitration
If two or more master-transmitters simultaneously start a transmission on the same bus, an arbitration
procedure is invoked. The arbitration procedure uses the data presented on the serial data bus
(I2Cx_SDA) by the competing transmitters.
illustrates the arbitration procedure between two
devices. The first master-transmitter, which drives I2Cx_SDA high, is overruled by another master-
transmitter that drives I2Cx_SDA low. The arbitration procedure gives priority to the device that transmits
the serial data stream with the lowest binary value. Should two or more devices send identical first bytes,
arbitration continues on the subsequent bytes.
If the I2C peripheral is the losing master, it switches to the slave-receiver mode, sets the arbitration lost
(AL) flag, and generates the arbitration-lost interrupt.
If during a serial transfer the arbitration procedure is still in progress when a repeated START condition or
a STOP condition is transmitted to I2Cx_SDA, the master-transmitters involved must send the repeated
START condition or the STOP condition at the same position in the format frame. Arbitration is not allowed
between:
•
A repeated START condition and a data bit
•
A STOP condition and a data bit
•
A repeated START condition and a STOP condition
Figure 22-12. Arbitration Procedure Between Two Master-Transmitters