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CHAPTER 17
IEBus CONTROLLER (
PD178096A, 178098A, 178F098 ONLY)
User’s Manual U12790EJ2V0UD
17.1.2 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 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
Broadcast communication (communication from one unit to multiple 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.
17.1.3 Communication mode
Although the IEBus has three communication modes each having a different transfer rate, the
PD178098A Subseries
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 17-1.
Table 17-1. 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. 18
Note The effective transfer rate when the maximum number of transfer bytes is transmitted (when fX = 6.3 MHz).
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
executed correctly.
17.1.4 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)