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CHAPTER 18 IEBus CONTROLLER (V850/SC2)
User’s Manual U15109EJ3V0UD
511
(4) Slave address field
The master outputs the address of the unit with which it is to communicate.
Figure 18-3 shows the configuration of the slave address field.
A parity bit is output after a 12-bit slave address has been transmitted in order to prevent a wrong slave
address from being received by mistake. Next, the master unit detects an acknowledge signal from the slave
unit to confirm that the slave unit exists on the bus. When the master has detected the acknowledge signal, it
starts outputting the control field. During broadcast communication, however, the master does not detect the
acknowledge bit but starts outputting the control field.
The slave unit outputs the acknowledge signal if its slave address matches and if the slave detects that the
parities of both the master address and slave address are even. The slave unit judges that the master address
or slave address has not been correctly received and does not output the acknowledge signal if the parities are
odd. At this time, the master unit is in the standby (monitor) status, and communication ends.
During broadcast communication, the slave address is used to identify group-unit broadcast or all-unit
broadcast, as follows:
If slave address is FFFH:
All-unit broadcast communication
If slave address is other than FFFH:
Group-unit broadcast communication
Remark
The group No. during group-unit broadcast communication is the value of the higher 4 bits of the
slave address.
If one unit occupies the bus as the master, the address set by the slave address register (SAR) is output.
Figure 18-3. Slave Address Field
Slave address field
Unit No.
MSB
LSB
ACK
Parity
Slave address (12 bits)
Group No.