UPD784938 Datasheet, PDF (471/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
(4) Slave address field
The master outputs the address of the unit with which it is to communicate.
Figure 20-3 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 coincides 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 high-order 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 20-3. Slave Address Field
Group No.
MSB
Slave address field
Slave address (12 bits)
Unit No.
Parity ACK
LSB
(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 20-4.
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 20-2 shows the contents of the control bits.
Preliminary User’s Manual U13987EJ1V0UM00
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