Inter-integrated Circuit (I2C) Interface
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249
SDA
SCL
S
START Condition
P
STOP Condition
Change of
data allowed
Change of
data allowed
Data line
stable
(Data valid)
Fig 13-4 START and STOP conditions
13.2.4.2
Addressing Slave Protocol
There are two address formats: the 7-bit address format and the 10-bit address format.
13.2.4.2.1
7-bit Address Format
During the 7-bit address format, the first seven bits (bits 7:1) of the first byte set the slave address and the LSB bit (bit 0) is the R/W bit as
shown in Fig 9-11. When bit 0 (R/W) is set to 0, the master writes to the slave. When bit 0 (R/W) is set to 1, the master reads from the slave.
S
A6
A5
A4
A3
A2
A1
A0
R/W
ACK
MSB
LSB
Slave Address
Sent by
slave
S = START condition
= Acknowledge
R/W = Read/Write Pulse
ACK
Fig 13-5 7-bit address format
13.2.4.2.2
10-bit Address Format
During 10-bit addressing, two bytes are transferred to set the 10-bit address. The transfer of the first byte contains the following bit definition.
The first five bits (bits 7:3) notify the slaves that this is a 10-bit transfer followed by the next two bits (bits 2:1), which set the slaves address bits
9:8, and the LSB bit (bit 0) is the R/W bit. The second byte transferred sets bits 7:0 of the slave address. Fig 9-12 shows the 10-bit address
format, and Table 13-1 defines the special purpose and reserved first byte addresses.
S
A8
R/W
A3
A2
A1
A0
ACK
S = START condition
= Acknowledge
R/W = Read/Write Pulse
ACK
1
1
1
1
0
A9
ACK
A6
A5
A4
A7
Sent by
slave
Sent by
slave
Fig 13-6 10-bit address format
Table 13-1 I
2
C definition of bits in the first byte
Slave Address
R/W Bit
Description
0000 000
0
General Call Address. I
2
C places the data in the receive buffer and issues a General Call
interrupt.
0000 000
1
START byte.
0000 001
X
CBUS address. I
2
C ignores these accesses.
0000 010
X
Reserved
0000 011
X
Reserved
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