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AD7682 Configuration problem

Question asked by jtm214 on Nov 19, 2012
Latest reply on Dec 5, 2012 by maithil

Hello,

I'm using the AD7682 ADC with a msp430 talking spi.  After a power I'm trying to configure the device but the configuration I'm reading back does not match the one I'm sending.  Here's what I'm sending:

0xFF70 (Which is 0x3FDC bit shifted left by 2 because of the 14 bit config register)

So I'm trying to set the following parameters:

bits

13          Overwrite Config

12:10     Unipolar, INx referenced to GND

9:7         IN3 is last conversion

6           Full BW

5:3        External reference, internal buffer, temp enabled

2:1        Scan 0:3 then temp

0           read back current config at the end of data

 

but this is what I'm receiving back from the device

0xE2E3

13       Overwrite Config

12:10  Unipolar, INx referenced to COM

9:7      channel (Don't care at this point)

6        1/4 BW

5:3      External reference, internal buffer, temperature disabled

2:1      Disable Sequencer

0         read back current config

 

So the process to get where I'm at is as follows:

Startup system

Configure SPI Port (4MHz clock, 8 bit data, etc)

create Rising edge on CNV line

Lower CNV

Write config

Read back config

Perform 2 dummy conversion

Read config

 

Is there anything wrong with the process I'm taking?  Am I correct in thinking that the 14 bit configuration register is left justifed (MSB first) on both the transmit and receive?  I'm trying to use the device in RAC mode and I've attached a screen shot of the SPI Comms.

Any help would be greatly appreciated.

Regards,

Justin

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