RL78/G1P
CHAPTER 12 SERIAL INTERFACE IICA
R01UH0895EJ0100 Rev.1.00
496
Nov 29, 2019
12.5.12 Arbitration
When several master devices simultaneously generate a start condition (when the STTn bit is set to 1 before the STDn
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 (ALDn) in the IICA status register n (IICSn)
is set (1) via the timing by which the arbitration loss occurred, and the SCLAn and SDAAn 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 ALDn = 1 setting that has been made by software.
For details of interrupt request timing, see
12.5.8 Interrupt request (INTIICAn) generation timing and wait control
.
Remark
STDn: Bit 1 of IICA status register n (IICSn)
STTn: Bit 1 of IICA control register n0 (IICCTLn0)
Figure 12-21. Arbitration Timing Example
SCLAn
SDAAn
SCLAn
SDAAn
SCLAn
SDAAn
Hi-Z
Hi-Z
Master 1 loses arbitration
Master 1
Master 2
Transfer lines
Remark
n = 0, 1