CS4218 datasheet(24/44 Pages) CIRRUS

24 / 44 page

Serial Control Port (SM4)

Serial Mode 4 separates the audio data from the

control data. Since control data such as gain and

attenuation do not change often, this mode re-

duces the bandwidth needed to support the audio

serial port.

The control information is entered through a

separate port that can be asynchronous to the

audio port and only needs to be updated when

changes in the control data are needed. After a

reset or power down, the control port must be

written once to initialize it if the port will be ac-

cessed to read or write control bits. This initial

write is considered a "dummy" write since the

data is ignored by the codec. A second write is

needed to configure the codec as desired. Then,

the control port only needs to be written to when

a change is desired, or to obtain the status infor-

mation. The control port does not function if the

master clock is not operating. When the control

port is used asynchronously to the audio port,

the noise performance may be slightly degraded

due to the asynchronous digital noise.

Since control data does not need to be accessed

each audio frame, an interrupt pin, MF5:INT, is

included in this mode and will go low when

status has changed. The control port serial data

format is illustrated in Figure 20. The control

port uses one of the multifunction pins as a chip

select line, MF4:CCS, that must be low for en-

tering control data. Although only 23 bits

contain useful data on MF2:CDIN, a minimum

of 31 bits must be written. If more than 31 bits

are written without toggling MF4:CCS, only the

first 31 are recognized. MF1:CDOUT contains

status information that is output on the rising

edge of MF3:CCLK. Status information is re-

p ea t ed at t h e e nd of t h e fr am e , bi ts 25

through 30, to allow a simple 8-bit shift and

latch register to store the most important status

information using the rising edge of MF4:CCS at

the latch control (see Appendix B).

Interrupt Pin - MF5:INT

Serial Mode 4 defines the multifunction pin

MF5:INT as an open-collector interrupt pin. In

SM4, this pin requires a pullup resistor and will

go low when the ADV bit or DI1 pin change, or

a rising edge on the LCL or RCL bits occurs, or

by exiting an SCLK out of range condition (Er-

ror = 3). The interrupt may be masked by setting

the MASK bit in the control serial data port.

MF5:INT is reset by reading the control serial

port.

MF4:CCS

MF3:CCLK

1 0 3

Err

Version

MF2:CDIN

MF1:CDOUT

00 0 1

Left

A/D Gain

Right

A/D Gain

Left

D/A Att.

Right

D/A Att.

Err

0 000 00 00

Figure 20. SM4 - Control Serial Port

CS4218

DS135F1

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