1
0 0 01
0 0 0
1 1
111
0
Device #1 loses arbitration
and switches off
Bus line
SCL
Data from
device #1
Data from
device #2
Bus line
SDA
Device #2 drives SDA
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I2C Module Operational Details
627
SPRUI07–March 2020
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Inter-Integrated Circuit Module (I2C)
If the I2C module is the losing master, it switches to the slave-receiver mode, sets the arbitration lost
(ARBL) flag, and generates the arbitration-lost interrupt request.
If during a serial transfer the arbitration procedure is still in progress when a repeated START condition or
a STOP condition is transmitted to 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 11-13. Arbitration Procedure Between Two Master-Transmitters
11.3.9 Digital Loopback Mode
The I2C module support a self-test mode called digital loopback, which is enabled by setting the DLB bit in
the I2CMDR register. In this mode, data transmitted out of the I2CDXR register is received in the I2CDRR
register. The data follows an internal path, and takes n cycles to reach I2CDRR, where:
n = 8 * (SYSCLK) / (I2C module clock (Fmod))
The transmit clock and the receive clock are the same. The address seen on the external SDA pin is the
address in the I2COAR register. Figure 11-14 shows the signal routing in digital loopback mode.
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