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CHAPTER 11 SERIAL INTERFACE FUNCTION
416
User’s Manual U15109EJ3V0UD
11.5.10 Arbitration
When several master devices simultaneously output a start condition (when STTn is set to 1 before STDn is set to
1
Note
), communication among the master devices is performed while the number of clocks are being adjusted until the
data differs. This kind of operation is called arbitration (n = 0, 1).
When one of the master devices loses in arbitration, an arbitration loss flag (ALDn) in IIC status register n (IICSn)
is set via the timing by which the arbitration loss occurred, and the SCLn and SDAn lines are both set to high
impedance, which releases the bus (n = 0, 1).
The arbitration loss is detected based on the timing of the next interrupt request (the eighth or ninth clock, when a
stop condition is detected, etc.) and the ALDn = 1 setting that has been made by software (n = 0, 1).
For details of interrupt request timing, see
11.5.5 I
2
C interrupt requests (INTIICn)
.
Note
STDn: Bit 1 of IIC status register n (IICSn)
STTn: Bit 1 of IIC control register n (IICCn)
Figure 11-31. Arbitration Timing Example
Master 1
Master 2
Transfer lines
SCLn
SDAn
SCLn
SDAn
SCLn
SDAn
Master 1 loses arbitration
Hi-Z
Hi-Z
Remark
n = 0, 1