UPD784938 Datasheet, PDF (469/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
20.1.5 Broadcasting communication
Normally, transmission or reception is performed between the master unit and its mating slave unit on a one-to-one basis.
During broadcasting communication, however, two or more slave units exist and the master unit executes transmission
to these slave units. Because plural slave units exist, the slave units do not return an acknowledge signal during
communication.
Whether broadcasting communication or normal communication is to be executed is selected by broadcasting bit (for
this bit, refer to 20.1.6 (2) Broadcasting request bit).
Broadcasting communication can be classified into the following two types:
(1) Group-unit broadcasting communication
Broadcasting communication is performed to the units in a group identified by the group number indicated by the high-
order 4 bits of the communication address.
(2) All-unit broadcasting communication
Broadcasting communication is performed to all the units, regardless of the value of the group number.
Group-unit broadcasting and all-unit broadcasting are identified by the value of the slave address (for the slave address,
refer to 20.1.6 (4) Slave address field).
20.1.6 Transmission format of IEBus
Figure 20-1 shows the transmission signal format of the IEBus.
Figure 20-1. IEBus Transmission Signal Format
Header
Master
address
field
Slave
address
field
Telegraph
Control field length
field
Data field
Frame format
Start
bit
Broad- Master Slave
casting address P address
bit bit
bit
PA
Control
bit
PA
Tele-
graph
length
PA
Data
bit
bit
PA
Data
bit
PA
Remarks 1. P: Parity bit, A: ACK/NACK bit
2. The master station ignores the acknowledge bit during broadcasting communication.
(1) Start bit
The start bit is a signal that informs the other units of the start of data transmission. The unit that is to start data
transmission outputs a high-level signal (start bit) from the TX pin for a specific time, and then starts outputting the
broadcasting bit.
If another unit has already output its start bit when one unit is to output the start bit, this unit does not output the start
bit but waits for completion of output of the start bit by the other unit. When the output of the start bit by the other unit
has completed, the unit starts outputting the broadcasting bit in synchronization with the completion of the start bit output
by the other unit.
The units other than the one that has started communication detect this start bit, and enter the reception status.
Preliminary User’s Manual U13987EJ1V0UM00
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