ATMEGA8_08 Datasheet, PDF (168/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

Figure 75. Arbitration Between Two Masters
START
SDA from
Master A
SDA from
Master B
SDA Line
Synchronized
SCL Line
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.
168 ATmega8(L)
2486T–AVR–05/08