CHAPTER 17 SERIAL INTERFACE IIC0 (
µ
PD780344Y, 780354Y SUBSERIES ONLY)
346
User’s Manual U15798EJ2V0UD
17.5.12 Arbitration
When several master devices simultaneously output a start condition (when STT0 is set to 1 before STD0 is set
to 1
Note
), 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) at the timing at 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
17.5.7 I
2
C interrupt requests (INTIIC0)
.
Note
STD0: Bit 1 of IIC status register 0 (IICS0)
STT0: Bit 1 of IIC control register 0 (IICC0)
Figure 17-15. Arbitration Timing Example
Master 1
Master 2
Transfer lines
SCL0
SDA0
SCL0
SDA0
SCL0
SDA0
Master 1 loses arbitration
Hi-Z
Hi-Z
