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Section 21 IEBus
TM
Controller
Page 1088 of 2108 R01UH0134EJ0400 Rev. 4.00
Sep 24, 2014
SH7262 Group, SH7264 Group
21.1.2 Communications Protocol
Figure 21.1 shows an IEBus transfer signal format.
Communications data is transferred as a series of signals referred to as a communications frame.
The number of data, which can be transmitted in a single communications frame and the transfer
speed, differs according to the communications mode.
(When IEBφ = 12, 18, 24, 30, or 36 MHz)
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 fieldMessage
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 21.1 Transfer Signal Format
(1) Header
A header is comprised of a start bit and a broadcast bit.
(a) Start Bit
The start bit is a signal to inform other units of the start of data transfer. A unit attempting to start
data transfer outputs a low-level signal (the 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 the start bit from the other unit without outputting its own start bit, and
then outputs the broadcast bit synchronized with the completion timing.
Other units enter the receive state after detecting the start bit.