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Trouble Configuring AD7738

Question asked by scarlson on Nov 17, 2015
Latest reply on Nov 30, 2015 by scarlson

Hi all,

 

First time poster here, long time chip user. 

 

I'm having some trouble getting my AD7738 to work (I do not have the eval kit).

 

I am not seeing anything on my DOUT.  Below is an view of DOUT, DIN, RDY, and CS.

 

to configure it I am sending in

 

0x00, 0xFF, 0xFF, 0xFF, 0xFF to reset it and then

 

0x01   IO port register, write

0xF0   Configure IO port register

0x2F   Channel setup register, AIN7, write

0x1C  Configure Channel setup register

0x37   Channel conversion time register, AIN7, write

0x91   Std. value

0x3F   Mode register, write (0x3F)

0x38   Continuous conversion, no clamp (0x38)

and then 0x4F every time RDY is polled.


but all I see is 0x00 in my rxbuffer, occasionally it goes 0xFF.

 

and the DOUT looks terrible.  I'm at a loss.

 

my pin configurations are also

 

SCLK -> SCLK

MCLKIN -> CMOS CLK @ 12MHz

MCLKUT -> OPEN

CS -> SS

RESET -> 5V

AVdd -> 5V

AINCOM/P0 -> OPEN (is this correct?)

SYNC/p1 -> OPEN (is this correct?)

AIN0-AIN7 -> AIN7 connected to signal generator

MUXOUT(+) -> ADCIN(+)

MUXOUT(-) -> ADCIN(-)

REFIN(+) -> 2.5V (about.. actually 2.38V)

REFIN(-) -> GND

AGN -> GND

RDY -> ISR set to detect inverted rising edge and send out 0x4F

DOUT -> MISO

DIN -> MOSI

DVdd -> 5V

DGND -> GND

 

I attached a graph for my 0x4F polling and for my initial setup.  the DOUT is sporadically working.. leading me to think I may have wired something wrong. 

 

Even more confusing, half the time the rxBuffer ISR won't be triggered and other times it will.. with identical code.

 

Any help at all would be great.  I am new to this chip and its kicking my **** and leaving me scratching my head.

 

thanks in advance,

scarlson

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