Datasheet

Section 14 IEBus™ Controller (IEB) [H8S/2258 Group]
Rev. 6.00 Mar. 18, 2010 Page 486 of 982
REJ09B0054-0600
PPAPAPAPA PA
1
Field name Header Master
address field
Slave address
field
Approximately 7330 μs
Approximately 2090 μs
Approximately 1590 μs
Approximately 1590 × N μs
Approximately 410 × N μs
Approximately 300 × N μs
Control field Data field
(When φ = 12 MHz)
Message
length field
Number
of bits
Transfer
time
Mode 0
Mode 1
Mode 2
Note: The value of acknowledge bit is ignored in broadcast communications.
P: Parity bit (1 bit)
A: Acknowledge bit (1 bit)
When A = 0: ACK
When A = 1: NAK
N: Number of bytes
1
Start
bit
Master
address
Slave
address
Control
bits
Data
bits
Data
bits
Message
length
bits
Broad-
cast
bit
1114 811 8118111112 12
Figure 14.2 Transfer Signal Format
(1) Header
Header is comprised of a start bit and a broadcast bit.
(a) Start Bit
The start bit is a signal for informing a start of data transfer to other units. A unit, which
attempts to start data transfer, outputs a low-level signal (start bit) for a specified period and
then outputs the broadcast bit.
If another unit is already outputting a start bit when a unit attempts to output a start bit, the unit
waits for completion of output of the start bit from the other unit without outputting the start
bit, and then outputs the broadcast bit synchronized with the completion timing.
Other units enter the receive state after detecting the start bit.
(b) Broadcast Bit
The broadcast bit is a bit to identify the type of communications: broadcast or normal.
When this bit is cleared to 0, it indicates the broadcast communications. When it is set to 1, it
indicates the normal communications. Broadcast communications includes group broadcast
and general broadcast, which are identified by a value of the slave address. (For details of the
slave address, see section 14.1.2 (3), Slave Address Field.)
Since there are multiple slave units, which are communications destination units, in the case of
broadcast communications, the acknowledge bit is not returned from each field described in (2)
and below.