ML51/ML54/ML56
Sep. 01, 2020
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ML51/M
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Series
Tec
hnical Reference
Manual
7-Bit Address with Data Format
6.12.3.2
Following the START condition is generated, one byte of special data should be transmitted by the
master. It includes a 7-bit long slave address (SLA) following by an 8
th
bit, which is a data direction bit
(R/W), to address the target slave device and determine the direction of data flow. If R/W bit is 0, it
indicates that the master will write information to a selected slave. Also, if R/W bit is 1, it indicates that
the master will read information from the addressed slave. An address packet consisting of a slave
address and a read I or a write (W) bit is called SLA+R or SLA+W, respectively. A transmission
basically consists of a START condition, a SLA+W/R, one or more data packets and a STOP
condition. After the specified slave is addressed by SLA+W/R, the second and following 8-bit data
bytes issue by the master or the slave devices according to the R/W bit configuration.
Figure 6.12-4 shows a master transmits data to slave by 7-bit. A master addresses a slave with a 7-bit
address and 1-bit write index to denote that the master wants to transmit data to the slave. The master
keeps transmitting data after the slave returns acknowledge to the master.
A = acknowledge (SDA low)
A = not acknowledge (SDA high)
S = START condition
P = STOP condition
‘0’ : write
S
SLAVE ADDRESS
R/W
A
DATA
A
DATA
A/A
P
from master to slave
from slave to master
data transfer
(n bytes + acknowlegde)
Figure 6.12-4 Master Transmits Data to Slave by 7-bit
Figure 6.12-5 shows a master read data from slave by 7-bit. A master addresses a slave with a 7-bit
address and 1-bit read index to denote that the master wants to read data from the slave. The slave
will start transmitting data after the slave returns acknowledge to the master.
‘1’ : read
S
SLAVE ADDRESS
R/W
A
DATA
A
DATA
A/A
P
data transfer
(n bytes + acknowlegde)
Figure 6.12-5 Master Reads Data from Slave
by 7-bit
There is an exception called “General Call” address, which can address all devices by giving the first
byte of data all 0. A General Call is used when a master wishes to transmit the same message to
several slaves in the system. When this address is used, other devices may respond with an
acknowledge or ignore it according to individual software configuration. If a device response the
General Call, it operates as like in the slave-receiver mode. Note that the address 0x00 is reserved for
General Call and cannot be used as a slave address, therefore, in theory, a 7-bit addressing I
2
C bus
accepts 127 devices with their slave addresses 1 to 127.
