Datasheet

Section 14 IEBus™ Controller (IEB) [H8S/2258 Group]
Rev. 6.00 Mar. 18, 2010 Page 484 of 982
REJ09B0054-0600
(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
A unit with the smallest master address has priority among units with the same
communications type.
Example: The master address is configured with 12 bits. A unit with H'000 has the highest
priority, and a unit with H'FFF has the lowest priority.
Note: When a unit loses arbitration, the unit can automatically enter retransfer mode (0 to 7
retransfer times can be selected by bits RN2 to RN0 in IEMCR).
(2) Communications Mode
The IEBus has three communications modes with different transfer speeds. Table 14.2 shows the
transfer speed in each communications mode and the maximum number of transfer bytes in one
communications frame.
Table 14.2 Transfer speed and Maximum Number of Transfer Bytes in Each
Communications Mode
Effective Transfer Speed
*
1
(kbps)
Communications
Mode
Maximum Number
of Transfer Bytes
(byte/frame) φ = 12 MHz
*
2
φ = 12.58 MHz
*
2
0 16 About 3.9 About 4.1
1 32 About 17 About 18
2 128 About 26 About 27
Notes: Each unit connected to the IEBus should select a communications mode prior to
performing communications. Note that correct communications is not guaranteed if the
master and slave units do not adopt the same communications mode.
In the case of communications between a unit with φ = 12 MHz and a unit with φ = 12.58
MHz, correct communications is not possible even if the same communications mode is
adopted. Communications must be performed at the same oscillation frequency.
1. An effective transfer speed when the maximum number of transfer bytes is transmitted.
2. Oscillation frequency when this LSI is used