ADC128S102: Wrong reading from channels.

Evgeny Erenburg

Prodigy 10 points

Part Number: ADC128S102

I read from ADC128S102. The diagram is following

SPI settings CPOL = 1, CPHA = 0

SPI MaserIn - pin DOUT

SPI MaseOut - pin DIN

SPI CLK - pin SCLK

ADC SS10 - pin CS

s_adc_latched val - is the value on a current channel

As you see CS goes low then I select all channel (IN0 - IN7) sequentially with 'SPI MaseOut' and on 'SPI MaserIn' I get a result .

I have a zoomed out look on channels IN1-IN2

The problem is - the values on channels are faulty - it's not what I measure with DMM on channels.

What can be a problem?

over 2 years ago

+1 Samiha Sharif over 2 years ago

TI__Genius 9716 points

Hi Evgeny,

Thanks for your question! Looking at the diagrams, it looks like the phases aren't synchronized. Could you try with SPI settings CPOL = 1, CPHA = 1? This should give you the correct value readings which match what you measure using a DMM on the channels. I hope this helps!

Best,

Samiha

+1 Evgeny Erenburg over 2 years ago in reply to Samiha Sharif

Prodigy 10 points

Thank you.

0 Evgeny Erenburg over 2 years ago in reply to Evgeny Erenburg

Prodigy 10 points

Well..I'm scanning two channels - IN0, IN1.

On IN0 the value 8EA (~2.3V)

On IN1 the value AC0 (~2.8V)

But actually it's quite opposite - on IN0 I measure 2.8v, on IN1 I measure 2.3v,

+1 Samiha Sharif over 2 years ago in reply to Evgeny Erenburg

TI__Genius 9716 points

Hi Evgeny,

Thanks for your question!

As the datasheet mentions in section 7.5.1, "While a conversion is in progress, the address of the next input for conversion is clocked into a control register through the DIN pin on the first 8 rising edges of SCLK after the fall of CS." and in Table 1, the conversion result of a conversion cycle is for the channel that was entered in the control register during the previous conversion cycle:

So 0AC0h is actually the result for IN0. I hope that helps!

Best,

Samiha

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ADC128S102: Wrong reading from channels.