3-5
Copyright 2008 Cirrus Logic, Inc.
DS732UM7
I2C Port
CS4953xx Hardware Users Manual
The number of bytes that can be transmitted per transfer is unrestricted. Data is transferred with the most-significant
bit (MSB) first. The first byte is an address byte that is always sent by the master after a Start or repeated Start
condition. This byte must be a 7-bit I
2
C slave a R/W bit. The 7-bit I
2
C address for the CS4953xx is
1000000b (0x80). The R/W bit is used to notify the slave if the current transaction is for the master to write data to
the slave (R/W = 0) or read data from the slave (R/W = 1).
After the master has sent the address byte, the master releases the SCP1_SDA line. If the slave received the address
byte, it will drive the SCP1_SDA line low to acknowledge (ACK) to the master that the byte was received. The
SCP1_SDA line must remain stable and low during the high period of the next clock pulse. When a slave doesn’t
acknowledge the slave address, the data line must be left high by the slave (NACK).
Figure 3-4. I
2
C Address with ACK and NACK
For write operations, the R/W bit must be set to zero (R/W = 0, Address = 0x80). After the 8-bit data byte has been
clocked, the master will release the SCP1_SDA line. If the slave received the byte correctly, it will drive the
SCP1_SDA line low for the next bit clock to acknowledge (ACK) that the data was received. If the data was not
received correctly, the slave can communicate this by leaving the SCP1_SDA line high (NACK).
For read operations, the R/W bit must be set to one (R/W = 1, Address = 0x81), then the master will read a data byte
from the slave. After the 8-bit data byte has been clocked, the master will release the SCP1_SDA line. If the master
received the byte correctly, it will drive the SCP1_SDA line low for the next bit clock to acknowledge (ACK) that
the data was received. If the data was not received correctly, the master can communicate this by leaving the
SCP1_SDA line high (NACK). The protocol on the last byte, however, is different. When the master receives the
last byte, it signals the end of the data to the slave by allowing SCP1_SDA to float high (NACK).
Start
SCP1_CLK
SCP1_SDA
A[6]
A[5]
A[4]
A[3]
A[2]
A[1]
A[0]
R/W
ACK
M
S
Start
SCP1_CLK
SCP1_SDA
A[6]
A[5]
A[4]
A[3]
A[2]
A[1]
A[0]
R/W
NACK
M
S
M = Master Drives SDA
S = Slave Drives SDA
Содержание CS4953xx
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