ATMEGA8_14 Datasheet, PDF (162/331 Pages) ATMEL Corporation – High-performance, Low-power Atmel

Figure 75. Arbitration Between Two Masters
START
SDA from
Master A
SDA from
Master B
SDA Line
Synchronized
SCL Line
ATmega8(L)
Master A Loses
Arbitration, SDA_A SDA
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
It is the user software’s responsibility to ensure that these illegal arbitration conditions never
occur. This implies that in multi-master systems, all data transfers must use the same composi-
tion of SLA+R/W and data packets. In other words: All transmissions must contain the same
number of data packets, otherwise the result of the arbitration is undefined.
2486AA–AVR–02/2013
162