dressed register (CDOUT will leave the high impedance state). If the MAP auto increment bit is
set to 1, the data for successive registers will appear consecutively.
2
5.7.2 I C Mode
In I²C mode, SDA is a bidirectional data line. Data is clocked into and out of the part by the clock,
SCL. There is no CS pin. Pins AD0 and AD1 form the two least significant bits of the chip ad-
dress and should be connected through a resistor to VLC or DGND as desired. The state of the
pins is sensed while the CS42438 is being reset.
The signal timings for a read and write cycle are shown in Figure 18 and Figure 19. A Start con-
dition is defined as a falling transition of SDA while the clock is high. A Stop condition is a rising
transition while the clock is high. All other transitions of SDA occur while the clock is low. The
first byte sent to the CS42438 after a Start condition consists of a 7 bit chip address field and a
R/W bit (high for a read, low for a write). The upper 5 bits of the 7-bit address field are fixed at
10010. To communicate with a CS42438, the chip address field, which is the first byte sent to
the CS42438, should match 10010 followed by the settings of the AD1 and AD0. The eighth bit
of the address is the R/W bit. If the operation is a write, the next byte is the Memory Address
Pointer (MAP) which selects the register to be read or written. If the operation is a read, the con-
tents of the register pointed to by the MAP will be output. Setting the auto increment bit in MAP
allows successive reads or writes of consecutive registers. Each byte is separated by an ac-
knowledge bit. The ACK bit is output from the CS42438 after each input byte is read, and is input
to the CS42438 from the microcontroller after each transmitted byte.
26
27 28
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19
24 25
SCL
SDA
DATA +1
DATA +n
CHIP ADDRESS (WRITE)
1 0 AD1 AD0
MAP BYTE
DATA
1
0
0
0
INCR
6
5
4
3
2
1
0
7
6
1
0
7
6
1
0
7
6
1
0
ACK
ACK
ACK
ACK
STOP
START
Figure 18. Control Port Timing, I²C Write
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
26 27 28
SCL
SDA
STOP
CHIP ADDRESS (WRITE)
AD1 AD0
MAP BYTE
CHIP ADDRESS (READ)
AD1 AD0
DATA
DATA +1 DATA + n
1
0
0
1
0
1
INCR
6
5
4
3
2
1
0
1
0
0
1
0
0
7
0
7
0
7
0
ACK
ACK
START
ACK
ACK
NO
ACK
START
STOP
Figure 19. Control Port Timing, I²C Read
Since the read operation can not set the MAP, an aborted write operation is used as a preamble.
As shown in Figure 19, the write operation is aborted after the acknowledge for the MAP byte
by sending a stop condition. The following pseudocode illustrates an aborted write operation fol-
lowed by a read operation.
Send start condition.
Send 10010xx0 (chip address & write operation).
Receive acknowledge bit.
DS646PP2
37
CIRRUS [ CIRRUS LOGIC ]
