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forcing ADC_SDATA to act as a PWM

Question asked by dimitris. on Nov 30, 2014
Latest reply on Dec 9, 2014 by JohnTo

Hi forum,

 

I am trying to force the I2S digital output (pin 26 on an ADAU1761) to output a PWM signal.

 

In order to succeed this I am forcing the I2S output to certain DC values by using DC sources in SigmaStudio.

Ideally, I would like to enable the first bit of the I2S output and then one by one add the rest of the 23 I2S bits. 

However, I am a bit confused on how the I2S values map to DC voltages.

 

I have figured out that a -1 DC voltage value will force the DIG0 to enable the MSB of the I2S output.

Then in order to keep  activating the rest of the I2S bits in a sequence I am using the values in the following table:

 

DC voltage value (5.23 format)I2S bit
below -1first MSB enabled
-1                   (-1/2^0)first MSB enabled
-0.5                (-1/2^1)first 2 MSB enabled
-0.25              (-1/2^2)first 3 MSB enabled
-0.125            (-1/2^3)first 4 MSB enabled
-0.0625          (-1/2^4)first 5 MSB enabled
-0.03125         (-1/2^5)first 6 MSB enabled
-0.015625        (-1/2^6)first 7 MSB enabled
?first 8 MSB enabled
?first 9 MSB enabled
?first 10 MSB enabled
...

...

 

however I cannot seem to activate more than 7 MSBs in a row. The DC voltage cannot output a value as low as necessary in order to activate the rest of the bits.

Any idea how I could activate the rest of the I2S bits?

How convention does SigmaStudio use in order to map the I2S data to DC values?

 

thanks

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