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Communication Problems with AD7734

Question asked by Moataz on Dec 21, 2014
Latest reply on Dec 26, 2014 by Moataz

Hello Every body.

Im trying since 3 Days to get a AD7734 working. ill describe the Problem and hope some one can help.


The AD7734 is connected with an atmega16 from atmel. REFIN(+), BIASHI and BIAS0 to BIAS3 are connected to 3.0V Ref. Voltage.

MCLKIN and MCLKOUT are connected to a 6.144 MHz Crystal like the application node page 31 in the device Datasheet.


on the oscilloscope i get followed Signals for MCLKIN and MCLKOUT (MCLKIN is blue).

Isn't the MCLKOUT too high. i mean with too large DC-Offset?


At MCU-Site (Source Code in Attatchments):

At first i reset the AD7734 by sending 4 Byted with the Value 0xff (like in example Code from AD). When i read the Revision-Register after that i get the Value 0x22. which is correct.


Then i configured the following Registers:


1- AD7734_REG_CH1_MODE : continuous conversion on channel 1, enable 24 bits mode.

     Byte1: 0x38     (Communication Register)

     Byte2: 0x22     (CH1 mode Register)


     Byte1: 0x28  (Communication Register)

     Byte2: 0x9     (CH1 Setup Register)

3-  AD7734_REG_CH1_CONVTIME: with the Value 10

     Byte1: 0x30 (Communication Reister)

     Byte2: 0x10 (CH1 Conversion Time Register)


When i try to read any one of those register after writing it i just get the Value 0x00. and i cant read the Value of CH1 because the RDY0 bit of the ADC status Register is always 0.


I Tried that with all 4 SPI Modes of the Controller. Specially the on that is described in the Datasheet of AD7734 . The spi Modes of the Atmel-MCU are in the following picture