Arbitration - NEC 78K0 Series User Manual

17.5.12 Arbitration

When several master devices simultaneously generate a start condition (when STT0 is set to 1 before STD0 is set
to 1), communication among the master devices is performed as the number of clocks are adjusted until the data
differs. This kind of operation is called arbitration.
When one of the master devices loses in arbitration, an arbitration loss flag (ALD0) in IIC status register 0 (IICS0)
is set (1) via the timing by which the arbitration loss occurred, and the SCL0 and SDA0 lines are both set to high
impedance, which releases the bus.
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 ALD0 = 1 setting that has been made by software.
For details of interrupt request timing, see 17.5.17 Timing of I
Remark STD0: Bit 1 of IIC status register 0 (IICS0)
STT0: Bit 1 of IIC control register 0 (IICC0)
Master 1
SCL0
SDA0
Master 2
SCL0
SDA0
Transfer lines
SCL0
SDA0
CHAPTER 17 SERIAL INTERFACE IIC0
Figure 17-19. Arbitration Timing Example
Preliminary User's Manual U17260EJ3V1UD
2
C interrupt request (INTIIC0) occurrence.
Hi-Z
Hi-Z
Master 1 loses arbitration
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