CHAPTER 19 IEBus CONTROLLER (V850/SB2)
User’s Manual U13850EJ6V0UD
546
(4) Slave address field
The master outputs the address of the unit with which it is to communicate.
Figure 19-3 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 broadcasting 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 broadcasting communication, the slave address is used to identify group-unit broadcasting or all-unit
broadcasting, as follows:
If slave address is FFFH:
All-unit broadcasting communication
If slave address is other than FFFH: Group-unit broadcasting communication
Remark
The group No. during group-unit broadcasting 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 19-3. Slave Address Field
Slave address field
Unit No.
MSB
LSB
ACK
Parity
Slave address (12 bits)
Group No.
(5) Control field
The master outputs the operation it requires the slave to perform, by using this field.
The configuration of the control field is as shown in Figure 19-4.
If the parity following the control bit is even and if the slave unit can execute the function required by the
master unit, the slave unit outputs an acknowledge signal and starts outputting the telegraph length field. If
the slave unit cannot execute the function required by the master unit even if the parity is even, or if the parity
is odd, the slave unit does not output the acknowledge signal, and returns to the standby (monitor) status.
The master unit starts outputting the telegraph field after confirming the acknowledge signal.
If the master cannot confirm the acknowledge signal, the master unit enters the standby status, and
communication ends. During broadcasting communication, however, the master unit does not confirm the
acknowledge signal, and starts outputting the telegraph length field.
Table 19-2 shows the contents of the control bits.
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