[AK4438]
(2) I2C-bus Control Mode (I2C pin = “H”)
The AK4438 supports the fast-mode I2C-bus (max: 400kHz, Ver1.0).
(2)-1. WRITE Operations
Figure 38 shows the data transfer sequence of the I2C-bus mode. All commands are preceded by a
START condition. A HIGH to LOW transition on the SDA line while SCL is HIGH indicates a START
condition (Figure 44). After the START condition, a slave address is sent. This address is 7 bits long
followed by the eighth bit that is a data direction bit (R/W). The most significant five bits of the slave
address are fixed as “00100”. The next bits are CAD1-0 (device address bits). These bits identify the
specific device on the bus. The hard-wired input pins (CAD1-0 pins) set these device address bits (Figure
39). If the slave address matches that of the AK4438, the AK4438 generates an acknowledge and the
operation is executed. The master must generate the acknowledge-related clock pulse and release the
SDA line (HIGH) during the acknowledge clock pulse (Figure 45). R/W bit = “1” indicates that the read
operation is to be executed. “0” indicates that the write operation is to be executed.
The second byte consists of the control register address of the AK4438. The format is MSB first, and
those most significant 3-bits are fixed to zeros (Figure 40). The data after the second byte contains control
data. The format is MSB first, 8bits (Figure 41). The AK4438 generates an acknowledge after each byte is
received. Data transfer is always terminated by a STOP condition generated by the master. A LOW to
HIGH transition on the SDA line while SCL is HIGH defines STOP condition (Figure 44).
The AK4438 can perform more than one byte write operation per sequence. After receipt of the third byte
the AK4438 generates an acknowledge and awaits the next data. The master can transmit more than one
byte instead of terminating the write cycle after the first data byte is transferred. After receiving each data
packet the internal address counter is incremented by one, and the next data is automatically taken into
the next address. If the address exceeds “14H” prior to generating a stop condition, the address counter
will “roll over” to “00H” and the previous data will be overwritten.
The data on the SDA line must remain stable during the HIGH period of the clock. The HIGH or LOW state
of the data line can only be changed when the clock signal on the SCL line is LOW (Figure 46) except for
the START and STOP conditions.
S
S
T
O
P
T
A
R
T
R/W="0"
Slave
Address
Sub
Address(n)
S
Data(n)
Data(n+1)
Data(n+x)
P
SDA
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
Figure 38. Data Transfer Sequence at the I2C-Bus Mode
0
0
1
0
0
CAD1 CAD0
R/W
(CAD1 and CAD0 are determined by pin settings)
Figure 39. The First Byte
0
0
0
A4
A3
A2
A1
D1
A0
D0
Figure 40. The Second Byte
D7
D6
D5
D4
D3
D2
Figure 41. Byte Structure After The Second Byte
016001925-E-00
2016/03
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AKM [ ASAHI KASEI MICROSYSTEMS ]
