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CHAPTER 17
IEBus CONTROLLER (
PD178096A, 178098A, 178F098 ONLY)
User’s Manual U12790EJ2V0UD
(4) Slave address field
The master outputs the address of the unit with which it is to communicate.
Figure 17-3 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 IEBus slave address register (SAR) is output.
Figure 17-3. 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 17-4.
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 broadcast communication, however, the master unit does not confirm the acknowledge signal, and
starts outputting the telegraph length field.
Table 17-2 shows the contents of the control bits.