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AS3668

Data Sheet - Detailed Description

Although the GPIO/AUDIO_IN pin supports digital output as well for simple control exercises an external pull up resistor is mandatory. The pin is

not able to actively drive the signal line because there is no push/pull stage integrated. The internal pull down resistor is disabled in audio

synchronization mode.

For a detailed description of music playback synchronization please refer to chapter 8.9.

8.8.1 Unused General Purpose Input / Output

If the pin is not used it is recommended to connect it to ground.

.

8.9 Audio Input

The audio input pin GPIO/AUDIO_IN is shared with a general purpose input/output. It is possible to switch the operating mode of the pin from a

GPIO to an analogue audio input. This multiplexed audio input pin allows the AS3668 to do lighting effects depending on the audio content

connected to GPIO/AUDIO_IN.

The block diagram for the signal processing path is shown in Figure 41. The analogue audio signal is coupled into the pin GPIO/AUDIO_IN with

an external DC blocking capacitor. The integrated audio pre-amplifier with automatic gain control attenuates or amplifies the input signal to avoid

clipping inside the signal processing path and furthermore increase the dynamic range of the signal in case a very small signal is applied to

AS3668. The AGC of the preamplifier uses the audio gain defined in register audio_gain as start value and changes the gain in a range of +/-

3dB. The pre-amplified audio signal is then feed into an special analogue signal processing unit to create special lighting effects. Various settings

inside the signal processing unit allow the user to define different types fancy lighting effects. This processing unit it directly linked together with

the control logic for the four current sources of the device. Thus, besides the ordinary lighting pattern control of the current sources with register

settings, the outputs are directly controlled in audio mode from the audio signal processing unit.

Table 25. GPIO Control Register

0x06 GPIO Control Register

Bit

Bit Name

Default

Access

Bit Description

2

gpio_in_invert

0

R/W

This bit allows the user to invert input signal of GPIO/AUDIO_IN if the pin is

configured as digital input.

0: Non-inverted digital input GPIO/AUDIO_IN

1: Inverted digital input GPIO/AUDIO_IN

1

gpio_in_en

1

R/W

0: GPIO/AUDIO_IN pin is configured as analog input (audio mode)

1: GPIO/AUDIO_IN pin is configured as digital input (general purpose)

0

gpio_mode

0

R/W

0: GPIO/AUDIO_IN pin is configured as input

1: GPIO/AUDIO_IN pin is configured as output in open drain configuration

The pin requires an external pull up resistor

Table 26. GPIO Signal Register

0x08 GPIO Signal Register

Bit

Bit Name

Default

Access

Bit Description

0

gpio_in

0R

The register is a read only register. The register is set to 1, if the pin GPIO/

AUDIO_IN is externally pulled high. The register is set to 0, if the pin is

connected to ground.

Table 27. GPIO Output Register

0x07 GPIO Output Register

Bit

Bit Name

Default

Access

Bit Description

0

gpio_out

0

R/W

This register is the output register if the pin GPIO/AUDIO_IN is configured as

output. Writing to the register changes the output state of the pin.

0: GPIO/AUDIO_IN pin low

1: GPIO/AUDIO_IN pin high (external pull-up resistor required)