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CHAPTER 18 IEBus CONTROLLER (V850/SC2)
User’s Manual U15109EJ3V0UD
509
18.1.5 Broadcast communication
Normally, transmission or reception is performed between the master unit and its mating 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 plural 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
18.1.6 (2) Broadcast bit
).
Broadcast communication can be classified into the two types; group-unit broadcast communication and all-unit
broadcast communication. Group-unit broadcast communication and all-unit broadcast communication are identified
by the value of the slave address (for the slave address, refer to
18.1.6 (4) Slave address field
).
(1) Group-unit broadcast communication
Broadcast communication is performed to 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 to all the units, regardless of the value of the group number.
18.1.6 Transfer format of IEBus
Figure 18-1 shows the transfer signal format of the IEBus.
Figure 18-1. IEBus Transfer Signal Format
Header
Master
address
field
Slave
address
field
Control field
Telegraph
length
field
Data field
Start
bit
Broad-
casting
bit
Master
address
bit
P
Frame format
Slave
address
bit
P A
Control
bit
P A
Tele-
graph
length
bit
P A
Data
bit
P A
Data
bit
P A
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 high-level signal (start bit) from the IETX0 pin for a specific time, and then starts outputting
the broadcast bit.
If another unit has already output its start bit when one unit attempts 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.