UPD6708 datasheet(9/72 Pages) NEC

9 / 72 page

µPD6708

2.2.3 Communication address

With the IEBus, a 12-bit communication address is assigned to each unit. The communication address is made up as

follows.

Higher 4 bits: Group number (number which identifies the group to which the unit belongs)

Lower 4 bits: Unit number (number which identifies a unit within a group)

2.2.4 Broadcast communication

In ordinary communication, there is only one master unit and one slave unit, and transmission or reception is performed

on an one-to-one basis. In broadcast communication, however, there are a number of slave units and the master unit

performs transmission with these slave units. Because there are several slave units, no acknowledge signals is returned

from the slave units during communication.

Whether broadcast communication or ordinary communication is performed is specified by the broadcast bit (for the

broadcast bit, see 2.3 (1) <2> “Broadcast bit”).

There are two kinds of broadcast communication, as follows.

(1) Group broadcast communication

Broadcast communication is performed to the units in a group whose group numbers are the same as that specified by

the higher 4 bits of the communication address.

(2) General broadcast communication

Broadcast communication is performed to all units irrespective of their group numbers.

Group broadcast communication or general broadcast communication is identified by the value of a salve address (for

the slave address, see 2.3 (3) “Slave address field”).

UPD6708 Datasheet(PDF) 9 Page - NEC