ISD3900
Publication Release Date: Dec 10, 2013
- 42 -
Revision 1.5
PWM_OUT
– Output signal to PWM.
DAC_OUT
– Output signal to AUXOUT/AUDOUT
I
2
S_OUT
– Output signal data to I
2
S interface
SPI_IN
– Input data from SPI. SPI_IN and DECODE cannot be both on at the same time. If
ENCODE is set, then an SPI record operation is selected. If not audio data is sent to the
signal path for a SPI DAC operation. Use the SPI_PCM_WRITE command to send audio data
to the ISD3900 from the SPI interface.
DECODE
– Used in conjunction with a play operation. When selected the signal path picks up
data from the compressor and plays it to the corresponding outputs selected.
I
2
S_IN
– Input data from I
2
S. I
2
S_IN and ADC_IN cannot be both on at the same time.
Table 12-13 CFG3 Register
CFG3 Configuration Register
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
VOLC[7:0]
Default 0x00:
0 dB attenuation to the output signal volume
Configuration register CFG3 sets the output signal volume. Setting 0 has 0dB attenuation. Each
subsequent step provides 0.25dB of attenuation.
Table 12-14 CFG4 Register
CFG4 Configuration Register
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
OFF_COMP
AGC_EN
ADC_IN
Default 0x00:
Disable the ADC input to the digital signal path.
Disable the Automatic Gain Control (AGC) for the ADC input.
Disable offset compensation on the ADC input.
Configuration register CFG4 controls the digital signal path functions:
ADC_IN
– Enables the ADC input to the digital signal path.
AGC_EN
– This bit enables the Automatic Gain Control (AGC) for the ADC input.
OFF_COMP
– This bit enables offset compensation on the ADC input. When enabled any DC
offset on the ADC input, whether from external sources or internal non-idealities is reduced to
zero. Offset compensation is recommended for correct AGC performance on small input
signals.
