
CHAPTER 18 IEBus CONTROLLER
User’s Manual U17790EJ2V0UD
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(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 ACK signal from the slave unit to
confirm that the slave unit exists on the bus. When the master has detected the ACK signal, it starts outputting
the control field. During broadcast communication, however, the master does not confirm the acknowledge bit
but starts outputting the control field.
The slave unit outputs the ACK 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 outputs the NACK 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 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 SAR register is output.
Figure 18-3. 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 18-4.
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 ACK 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 outputs the NACK signal, and returns to the standby (monitor) status.
The master unit starts outputting the telegraph field after detecting the ACK signal.
If the master can detect the NACK signal, the master unit enters the standby status, and communication ends.
During broadcast communication, however, the master unit does not confirm the acknowledge bit, and starts
outputting the telegraph length field.
The contents of the control bits are shown below.