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Section 21 IEBus
TM
Controller
R01UH0134EJ0400 Rev. 4.00 Page 1085 of 2108
Sep 24, 2014
SH7262 Group, SH7264 Group
(1) Determination of Bus Mastership (Arbitration)
A unit connected to the IEBus performs an operation to get the bus to control other units. This
operation is called arbitration. In arbitration, when multiple units start transferring simultaneously,
the bus mastership is given to one unit among them.
Only one unit can obtain bus mastership through arbitration, so the following priority for bus
mastership is determined.
(a) Priority according to communications type
Broadcast communications (one-to-many communications) has priority over normal
communications (one-to-one communications).
(b) Priority according to master address
The unit with the smallest master address has priority among units of the same communications
type.
Example: The master address is configured with 12 bits. A unit with H'000 has the highest
priority, while a unit with H'FFF has the lowest priority.
Note: When a unit loses in arbitration, the unit can automatically enter retransfer mode (0 to 7
retransfer times can be selected by the RN bit in IEMCR).