CHAPTER 19 IEBus CONTROLLER (V850/SB2)
User’s Manual U13850EJ4V0UM
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(6) Communication scale
The communication scale of IEBus is as follows:
•
Number of units: 50 MAX.
•
Cable length:
150 m MAX. (when twisted pair cable is used)
Caution The communication scale in an actual system differs depending on the characteristics of
the cables, etc., constituting the IEBus driver/receiver and IEBus.
19.1.2 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 is used to grant 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 conditions of the bus are
predetermined as follows:
Caution The bus mastership is released if communication is aborted.
(1) Priority by communication type
Broadcasting 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.
19.1.3 Communication mode
Although the IEBus has three communication modes each having a different transfer rate, the V850/SB2 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 19-1.
Table 19-1. Transfer Rate and Maximum Number of Transfer Bytes in Communication Mode 1
Communication Mode
Maximum Number of Transfer Bytes (Bytes/Frame)
Effective Transfer Rate (Kbps)
Note
1
32
Approx. 17
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 partner unit (slave unit) are not the same, communication
is not correctly executed.
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