Datasheet

M-Bus Module
MOTOROLA MCF5206e USER’S MANUAL 13-3
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1
NOTE
For further information on M-Bus system configuration, protocol,
and restrictions please refer to the Philip’s I
2
C Standard
13.4 M-BUS PROTOCOL
Normally, a standard communication is composed of four parts: (1) START signal, (2) slave
address transmission, (3) data transfer, and (4) STOP signal. They are described briefly in
the following sections and illustrated in Figure 13-2.
13.4.1 START Signal
When the bus is free, i.e., no master device is engaging the bus (both SCL and SDA lines
are at logic high), a master can initiate communication by sending a START signal. As
shown in Figure 13-2, a START signal is defined as a high-to-low transition of SDA while
SCL is high. This signal denotes the beginning of a new data transfer (each data transfer
can contain several bytes of data) and awakens all slaves.
13.4.2 Slave Address Transmission
The first byte of data transferred by the master immediately after the START signal is the
slave address. This is a seven-bit calling address followed by a R/W bit. The R/W bit tells
the slave data transfer direction. No two slaves in the system can have the same address.
Figure 13-2. M-Bus Standard Communication Protocol
123
45678
12345678
SCL 12345678 12 567834
9 9
AD7 AD6
AD5
AD4 AD3 AD2
AD1 R/W
XXX D7 D6 D5 D4 D3 D2 D1 D0
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W AD7 AD6
AD5
AD4 AD3 AD2 AD1 R/W
99
XX
NEW CALLING ADDRESS
READ/WRITE
NO
ACK
BIT
STOP
SIGNAL
REPEATED
START
SIGNAL
ACK
BIT
READ/
WRITE
CALLING ADDRESS
START
SIGNAL
SDA
MSB LSB
START
SIGNAL
CALLING ADDRESS
READ/
WRITE
ACK
BIT
MSB
LSB
DATA BYTE
NO
ACK
BIT
STOP
SIGNAL
LSBMSBLSBMSB
SDA
SCL
Fr
eescale S
emiconduct
or
, I
Freescale Semiconductor, Inc.
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