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CHAPTER 17
IEBus CONTROLLER (
PD178096A, 178098A, 178F098 ONLY)
User’s Manual U12790EJ2V0UD
17.1.5 Broadcast communication
Normally, transmission or reception is performed between the master unit and its partner slave unit on a one-to-one
basis. During broadcast communication, however, two or more slave units exist and the master unit executes transmission
to these slave units. Because multiple slave units exist, the slave units do not return an acknowledge signal during
communication.
Whether broadcast communication or normal communication is to be executed is selected by the broadcast bit (for this
bit, refer to 17.1.6 (2) Broadcast bit).
Broadcast communication is classified into two types: group-unit broadcast communication and all-unit broadcast
communication. Group-unit broadcast and all-unit broadcast are identified by the value of the slave address (for the slave
address, refer to 17.1.6 (4) Slave address field).
(1) Group-unit broadcast communication
Broadcast communication is performed with the units in a group identified by the group number indicated by the
higher 4 bits of the communication address.
(2) All-unit broadcast communication
Broadcast communication is performed with all the units, regardless of the value of the group number.
17.1.6 Transfer format of IEBus
Caution The logic on the IEBus I/O pin of the
PD178098A Subseries and the logic of the IEBus protocol
(data on the IEBus) are inverted values. The following describes the case of the IEBus protocol.
<Example: Start bit>
PD178098A:
High level
 IEBus protocol: Low level
Figure 17-1 shows the transfer signal format of the IEBus.
Figure 17-1. IEBus Transfer Signal Format
Remarks 1. P: Parity bit, A: ACK/NACK bit
2. The master station ignores the acknowledge bit during broadcast communication.
(1) Start bit
The start bit is a signal that informs the other units of the start of data transfer.
The unit that is to start data transfer outputs a low-level signal (start bit) for a specific time, and then starts
outputting the broadcast bit.
If another unit has already output its start bit when one unit is to output the start bit, this unit does not output
the start bit but waits for completion of output of the start bit by the other unit. When the output of the start bit
by the other unit is complete, the unit starts outputting the broadcast bit in synchronization with the completion
of the start bit output by the other unit.
The units other than the one that has started communication detect this start bit, and enter the reception status.
Header
Master
address
field
Slave
address
field
Control field
Telegraph
length
field
Data field
Start
bit
Broad-
cast
bit
Master
address
bit
P
Frame format
Slave
address
bit
PA
Control
bit
PA
Tele-
graph
length
bit
PA
Data
bit
PA
Data
bit
PA