Figure 98. Arbitration Between Two Masters
START
Master A Loses
Arbitration, SDAA SDA
SDA from
Master A
SDA from
Master B
SDA Line
Synchronized
SCL Line
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 composition 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.
246
ATmega640/1280/1281/2560/2561
2549A–AVR–03/05
ATMEL [ ATMEL ]
