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19.1.6 Transfer format of IEBus
Figure 19-1 shows the transfer signal format of the IEBus.
Frame format
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 transfer. The unit that is to start data
transfer outputs a high-level signal (start bit) from the IETX 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 is complete, 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.
(2) Broadcasting bit
This bit indicates whether the master selects one slave (individual communication) or plural slaves
(broadcasting communication) as the other party of communication.
When the broadcasting bit is 0, it indicates broadcasting communication; when it is 1, individual
communication is indicated.
communication and all-unit communication. These communication types are identified by the value of the
slave address (for the slave address, refer to 19.1.6 (4) Slave address field).
Because two or more slave units exist in the case of broadcasting communication, the acknowledge bit in
each field subsequent to the master address field is not returned.
If two or more units start transmitting a communication frame at the same time, broadcasting communication
takes precedence over individual communication, and wins in arbitration.
If one station occupies the bus as the master, the value set to the broadcasting request bit (ALLRQ) of the
IEBus control register (BCR) is output.
544
CHAPTER 19
IEBus CONTROLLER (V850/SB2)
Figure 19-1. IEBus Transfer Signal Format
Master
Slave
address
address
Header
field
field
Broad-
Master
Slave
Start
casting
address
address
P
bit
bit
bit
bit
Broadcasting communication is classified into two types: group-unit
User's Manual U13850EJ6V0UD
Telegraph
length
Control field
field
Tele-
Control
Data
graph
P A
P A
P A
length
bit
bit
bit
Data field
Data
P A
P A
bit
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