Embedded Target for Texas Instruments C6000 DSPs

C6711 DSK ADC

Configure digitized signal output from the codec to the processor

Library

c6711dsklib in Embedded Target for TI C6000 DSP

Description

Use the C6711 DSK ADC (analog-to-digital converter) block to capture and digitize analog signals from external sources, such as signal generators, frequency generators or audio devices. Placing an C6711 DSK ADC block in your Simulink block diagram lets you use the audio coder-decoder module (codec) on the C6711 DSK to convert an analog input signal to a digital signal for the digital signal processor.

Most of the configuration options in the block affect the codec. However, the Output data type, Samples per frame and Scaling options are related to the model you are using in Simulink, the signal processor on the board, or direct memory access (DMA) on the board. In the following table, you find each option listed with the C6711 DSK hardware affected.

Option	Affected Hardware
ADC Source	Codec
Mic	Codec
Output data type	TMS320C6701 digital signal processor
Samples per frame	Direct memory access functions
Scaling	TMS320C6701 digital signal processor
Source gain (dB)	Codec

You can select one of three input sources from the ADC source list:

• Line In -- the codec accepts input from the line in connector (LINE IN) on the board's mounting bracket.
• Mic -- the codec accepts input from the microphone connector (MIC IN) on the board mounting bracket.
• Loopback -- routes the analog signal from the codec output back to the codec input. Can be useful in some feedback applications.

Use the Stereo check box to indicate whether the audio input is monaural or stereo. Clear the check box to choose monaural audio input. Select the check box to enable stereo audio input. Monaural (mono) input is left channel only, but the output sends left channel content to both the left and right output channels; stereo uses the left and right channels. Table 6-1, Audio Word Byte Order for Mono and Stereo Inputs, shows how the codec stores monaural and stereo digitized signals in 32-bit words on the C6711 DSK. In the table, L means left channel, R means right channel, and O means that the 4-byte nibble does not contain data.

Table 6-6: Audio Word Byte Order for Mono and Stereo Inputs 

Format	Left and Mono Channel (first 16 bits of data word)	Right and Stereo Channel (last 16 bits of data word)
16-bit mono	0xLLLL	0x0000
16-bit stereo	0xLLLL	0xRRRR
8-bit mono	0xLL00	0x0000
8-bit stereo	0xLL00	0xRR00
4-bit mono	0xL000	0x0000
4-bit stereo	0xL000	0xR000

When you select Mic for ADC source, you can select the +20 dB Mic gain boost check box to add 20 dB to the microphone input signal before the codec digitizes the signal.

Selecting Loopback for ADC source configures the C6711 DSK to capture the output from the codec as the input to the C6701 EVM ADC. When you select Loopback, your model must include both the C6701 EVM ADC and C6701 EVM  DAC blocks.

Source gain (dB) lets you add gain to the input signal before the A/D conversion. When you select Loopback as the ADC source, your specified source gain is not added to the input signal. Select the appropriate gain from the list.

Dialog Box

ADC source

The input source to the codec. Line In is the default.

+20 dB Mic gain boost

Boosts the input signal by +20dB when ADC source is Mic. Gain is applied before analog-to-digital conversion.

Output data type

Selects the word length and shape of the data from the codec. By default, double is selected. Options are Double, Single, and Integer

Scaling

Selects whether the codec data is unmodified, or normalized to the output range to ±1.0, based on the codec data format. Select either Normalize or Integer Value. Normalize is the default setting.

Source gain (dB)

Specifies the amount to boost the input before conversion. Select from the range 0.0 to 12.0 dB in 1.5 dB increments. Applies to the input signal when ADC source is Line In or Mic In.

Samples per frame

Creates frame-based outputs from sample-based inputs. This parameter specifies the number of samples of the signal the block buffers internally before it sends the digitized signals, as a frame vector, to the next block in the model. 64 samples per frame is the default setting. Notice that the frame rate depends on the sample rate and frame size. For example, if your input is 32 samples per second, and you select 64 samples per frame, the frame rate is one frame every two seconds. The throughput remains the same at 32 samples per second.

See Also
C6711 DSK DAC

C6701 EVM RESET

C6711 DSK DAC