
370
CHAPTER 17
IEBus CONTROLLER (
PD178096A, 178098A, 178F098 ONLY)
User’s Manual U12790EJ2V0UD
(2) Broadcast bit
This bit indicates whether the master selects one slave (individual communication) or multiple 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 17.1.6
(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 unit occupies the bus as the master, the value set to the broadcast request flag (ALLRQ) of IEBus control
register 0 (BCR0) 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 17-2.
If two or more units start transmitting the broadcast bit at the same time, the master address field is used to make
a judgment of arbitration.
The data output in the master address field is compared with the data on the bus each time one bit is output.
If the master address output in 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 the master
unit.
Next, this master unit outputs a parity bit, determines the master address of other units, 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.
Figure 17-2. Master Address Field
Master address field
Master address (12 bits)
MSB
LSB
Parity