Datasheet

Section 14 IEBus™ Controller (IEB) [H8S/2258 Group]
Rev. 6.00 Mar. 18, 2010 Page 483 of 982
REJ09B0054-0600
14.1.1 IEBus Communications Protocol
The overview of the IEBus is described below.
• Communications method: Half duplex asynchronous communications
• Multi-master system
All units connected to the IEBus can transfer data to other units.
• Broadcast communications function (one-to-many communications)
⎯ Group broadcast communications: Broadcast communications to group unit
⎯ General broadcast communications: Broadcast communications to all units
• Mode is selectable (three modes with different transfer speeds).
Table 14.1 Mode Types
Mode φ = 12 MHz φ = 12.58 MHz
Maximum Number of
Transfer Bytes (byte/frame)
0 About 3.9 kbps About 4.1 kbps 16
1 About 17 kbps About 18 kbps 32
2 About 26 kbps About 27 kbps 128
• Access control: CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
Priority of bus mastership is as follows.
⎯ Broadcast communications (one-to-many communications) have priority rather than
normal communications (one-to-one communications).
⎯ Smaller master address has priority.
• Communications scale
⎯ Number of units: Up to 50
⎯ Cable length: Up to 150 m (when using a twisted pair cable)
Note: The communications scale of the actual system depends on the externally mounted IEBus
driver/receiver characteristics and the characteristics of the cable to be used.
(1) Determination of Bus Mastership (Arbitration)
A unit connected to the IEBus performs an operation for getting the bus to control other units.
This operation is called arbitration. In arbitration, when the multiple units start transfer
simultaneously, the bus mastership is given to one unit among them.
Only one unit can get bus mastership through arbitration, so the following priority for bus
mastership is defined.