Specifications

Appendix B: Applications of SM4
Figure B1 illustrates one method of using Serial Mode 4 wherein a DSP controls the audio serial port
and a microcontroller controls the control port. Each controller is run independently and the micro
updates the control information only when needed, or when an interrupt from the CS4218 occurs.
Figure B2 illustrates the minimum interface to the CS4218. In this application, the DSP sends and
receives stereo DAC and ADC information. The CS4218 is configured for 32 bits per frame, Master
sub-mode. The control data resets to all zeros, which configures the CS4218 as a simple stereo codec:
no gain, no attenuation, line inputs #1, and DAC outputs not muted.
Figure B3 illustrates how to use all the CS4218 features with a low cost DSP that cannot support the
interrupt rate of SM3. Using SM4 (32 bits per frame, Master sub-mode) reduces the DSP interrupts in
half since the control data is split from the audio data. This circuit is comprised of three independent
sections which may individually be eliminated if not needed.
Micro-
Controller
Serial
Port
General
Purpose
Port
Pins
IRQ
DSP
SDOUT
SDIN
SSYNC
SCLK
CS4218
MF1:CDOUT
MF2:CDIN
MF4:CCS
MF3:CCLK
RESET
MF8:F3
MF7:F2
MF6:F1
MF5:INT
SM4
VD+
43
42
1
44
40
39
36
35
38
2
34
31
30
Figure B1. SM4 - Microcontroller Interface
DSP
SDOUT
SDIN
SSYNC
SCLK
CS4218
MF1:CDOUT
MF2:CDIN
MF4:CCS
MF3:CCLK
MF5:INT
SM4
VD+
RESET
MF8:F3
MF7:F2
MF6:F1
Hard Wired or
DIP Switch
selectable
32 BPF
43
42
1
44
35
36
38
40
39
2
34
31
30
Figure B2. SM4 - Minimum DSP Interface
CS4218
40 DS135F1