RL78/G13 CHAPTER 13 SERIAL INTERFACE IICA
R01UH0146EJ0100 Rev.1.00 731
Sep 22, 2011
13.5.12 Arbitration
When several master devices simultaneously generate a start condition (when the STT0 bit is set to 1 before the STD0
bit 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 the IICA status register 0 (IICS0)
is set (1) via the timing by which the arbitration loss occurred, and the SCLA0 and SDAA0 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 13.5.8 Interrupt request (INTIICA0) generation timing and wait control.
Remark STD0: Bit 1 of IICA status register 0 (IICS0)
STT0: Bit 1 of IICA control register 00 (IICCTL00)
Figure 13-21. Arbitration Timing Example
SCLA0
SDAA0
SCLA0
SDAA0
SCLA0
SDAA0
Hi-Z
Hi-Z
Master 1 loses arbitration
Master 1
Master 2
Transfer lines
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