Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
212
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
Figure 22-7.
SCL Synchronization Between Multiple Masters
Arbitration is carried out by all masters continuously monitoring the SDA line after outputting data. If the value
read from the SDA line does not match the value the Master had output, it has lost the arbitration. Note that a
Master can only lose arbitration when it outputs a high SDA value while another Master outputs a low value. The
losing Master should immediately go to Slave mode, checking if it is being addressed by the winning Master.
The SDA line should be left high, but losing masters are allowed to generate a clock signal until the end of the
current data or address packet. Arbitration will continue until only one Master remains, and this may take many
bits. If several masters are trying to address the same Slave, arbitration will continue into the data packet.
read from the SDA line does not match the value the Master had output, it has lost the arbitration. Note that a
Master can only lose arbitration when it outputs a high SDA value while another Master outputs a low value. The
losing Master should immediately go to Slave mode, checking if it is being addressed by the winning Master.
The SDA line should be left high, but losing masters are allowed to generate a clock signal until the end of the
current data or address packet. Arbitration will continue until only one Master remains, and this may take many
bits. If several masters are trying to address the same Slave, arbitration will continue into the data packet.
Figure 22-8.
Arbitration Between Two Masters
Note that arbitration is not allowed between:
A REPEATED START condition and a data bit.
A STOP condition and a data bit.
A REPEATED START and a STOP condition.
TA
low
TA
high
SCL from
Master A
SCL from
Master B
SCL Bus
Line
TB
low
TB
high
Masters Start
Counting Low Period
Masters Start
Counting High Period
SDA from
Master A
SDA from
Master B
SDA Line
Synchronized
SCL Line
START
Master A Loses
Arbitration, SDA
A
SDA