NEC Renesas V850/SC1 User Manual page 512

(2) Broadcast bit
This bit indicates whether the master selects one slave (individual communication) or plural slaves (broadcast
communication) as the other party of communication.
When the broadcast bit is 0, it indicates broadcast communication; when it is 1, individual communication is
indicated. Broadcast communication is classified into two types: group-unit communication and all-unit
communication. These communication types are identified by the value of the slave address (for the slave
address, refer to 18.1.6 (4) Slave address field).
Because two or more slave units exist in the case of broadcast communication, the acknowledge bit in each
field subsequent to the master address field is not returned.
If two or more units start transmitting a communication frame at the same time, broadcast communication
takes precedence over individual communication, and wins in arbitration.
If one station occupies the bus as the master, the value set to the broadcast request bit (ALLRQ) of the IEBus
control register (BCR) is output.
(3) Master address field
The master address field is output by the master to inform a slave of the master's address.
The configuration of the master address field is as shown in Figure 18-2.
If two or more units start transmitting the broadcast bit at the same time, the master address field makes a
judgment of arbitration.
The master address field compares the data it outputs with the data on the bus each time it has output one bit.
If the master address output by the master address field is found to be different from the data on the bus as a
result of comparison, it is assumed that the master has lost in arbitration. As a result, the master stops
transmission and enters the reception status.
Because the IEBus is configured of wired AND, the unit having the minimum master address of the units
participating in arbitration (arbitration masters) wins in arbitration.
After a 12-bit master address has been output, only one unit remains in the transmission status as one master
unit.
Next, this master unit outputs a parity bit, determines the master address of the other unit, and starts outputting
a slave address field.
If one unit occupies the bus as the master, the address set by the IEBus unit address register (UAR) is output.
MSB
510
CHAPTER 18 IEBus CONTROLLER (V850/SC2)
Figure 18-2. Master Address Field
Master address field
Master address (12 bits)
User's Manual U15109EJ3V0UD
Parity
LSB