Cirrus Logic CS4245 - Manual (Page 38)

38 DS656F3
CS4245
dress and set the read/write bit (R/W) high. The next falling edge of CCLK will clock out the MSB of the
addressed register (CDOUT will leave the high-impedance state).
For both read and write cycles, the memory address pointer will automatically increment following each
data byte in order to facilitate block reads and writes of successive registers.
4.12.2 I²C 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 address and should
be connected through a resistor to VLC or DGND as desired. The state of the pins is sensed while the
CS4245 is being reset.
The signal timings for a read and write cycle are shown in Figure 18 and Figure 19 . A Start condition 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 CS4245
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 10011. To communicate with a CS4245, the chip
address field, which is the first byte sent to the CS4245, should match 10011 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 contents of the register pointed to by the MAP will be output. Following each data byte, the mem-
ory address pointer will automatically increment to facilitate block reads and writes of successive regis-
ters. Each byte is separated by an acknowledge bit. The ACK bit is output from the CS4245 after each
input byte is read, and is input to the CS4245 from the microcontroller after each transmitted byte.
M A P
MSB LSB
DATA
b y te 1 b y te n
R/W R/W
A D D R E S S
C H IP
ADDRESS
C H IP
C D IN
C C L K
CS
C D O U T
MSB LSB MSB LSB
1001111 1001111
MAP = Memory Address Pointer, 8 bits, MSB first
High Impedance
Figure 17. Control Port Timing in SPI Mode
4 5 6 7 24 25
SCL
CHIP ADDRESS (WRITE) MAP BYTE DATA DATA +1
START
ACK
STOP
ACK ACK ACK
1 0 0 1 1 AD1 AD0 0 SDA 6 6 5 4 3 2 1 0 7 6 1 0 7 6 1 0 7 6 1 0
0 1 2 3 8 9 12 16 17 18 19 10 11 13 14 15 27 28 26
DATA +n
Figure 18. Control Port Timing, I²C Write