Determination Of Bus Mastership (Arbitration); Communication Mode; Communication Address - NEC Renesas V850/SC1 User Manual

18.1.2 Determination of bus mastership (arbitration)

An operation to occupy the bus is performed when a unit connected to the IEBus controls the other units. This
operation is called arbitration.
When two or more units simultaneously start transmission, arbitration grants one of the units the permission to
occupy the bus.
Because only one unit is granted the bus mastership as a result of arbitration, the priority condition of the bus is
predetermined as follows:
Caution The bus mastership is released if communication is aborted.
(1) Priority by communication type
Broadcast communication (communication from one unit to plural units) takes precedence over normal
communication (communication from one unit to another).
(2) Priority by master address
If the communication type is the same, communication with the lower master address takes precedence.
A master address consists of 12 bits, with unit 000H having the highest priority and unit FFFH having the
lowest priority.

18.1.3 Communication mode

Although the IEBus has three communication modes each having a different transfer rate, the V850/SC2 supports
only communication mode 1. The transfer rate and the maximum number of transfer bytes in one communication
frame in communication mode 1 are as shown in Table 18-1.
Table 18-1. Transfer Rate and Maximum Number of Transfer Bytes in Communication Mode 1
Communication Mode
1
Note The effective transfer rate when the maximum number of transfer bytes is transmitted.
Select the communication mode (mode 1) for each unit connected to the IEBus before starting communication. If
the communication mode of the master unit and that of the mating unit (slave unit) are not the same, communication is
not correctly executed.

18.1.4 Communication address

With the IEBus, each unit is assigned a specific 12-bit address. This communication address consists of the
following identification numbers:
• Higher 4 bits: Group number (number to identify the group to which each unit belongs)
• Lower 8 bits:
Unit number (number to identify each unit in a group)
508
CHAPTER 18 IEBus CONTROLLER (V850/SC2)
Maximum Number of Transfer Bytes (Bytes/Frame)
32
User's Manual U15109EJ3V0UD
Effective Transfer Rate (Kbps)
Approx. 17
Note