AD7731 Issue

Hello all,

I am pulling my hair out. I cannot get any communication from either of the 2 AD7731 ADCs I have. I am creating a new hardware rev of a water sanitation system. The OLD hardware was AD7731 and Atmel128. New hardware is AD7731 and PIC18f45k22.

I have ported the code from the atmel to the PIC. I am confident in the Code as I can talk to other SPI devices on the board just fine. As for the AD7731 I cannot get any response from the IC at all. No !RDY pin low, no ability to read the registers, etc. !RDY stays high at all times. I received the parts as Analog.com samples. The !RDY pin NEVER goes LOW. No matter how long I wait.

Here are snippets of my setup and communication code.

// Initialize SPI
// MCU is running @32Mhz, divide FOSC/64 to run SPI @ 500Khz.
//(Have tried, 2Mhz, 4Mhz, and 8Mhz)
SPI1_Init_Advanced(_SPI_MASTER_OSC_DIV64, _SPI_DATA_SAMPLE_MIDDLE, _SPI_CLK_IDLE_LOW, _SPI_LOW_2_HIGH);


void Setup_AD7731(void){
write_register(0x03, 0x13, 0x34); //Initialize filter register.

// Self calibrate millivolt input (Electrode Inputs)
/*----------------------------------------------------------------------------*/
// Calibrate Zero point
write_register(0x02, 0x90, 0xF6); //Self calibrate mV input zero.
while(AD7731_DR != LOW); //Wait for the ready pin to go low.

// Set to Full Scale
write_register(0x02, 0xB0, 0xF6); //Self calibrate mV input full scale.
while(AD7731_DR != LOW); //Wait for the ready pin to go low.
}
}


void write_register(char reg, char msb, char lsb)
{

SELECT_AD7731; //Select the a/d converter.
SPI1_Write(reg); //Select the required a/d register.
SPI1_Write(msb); //Send msb byte.
SPI1_Write(lsb); //Send lsb byte.
DISABLE_AD7731; //De-select a/d converter.

}




This is a direct port from a working system. I am loosing my mind here. Anyone see what I am doing wrong?

Do you have a clock at the A/D oscillator output?

Do you have the SPI clock edge and polarity set correctly to match the A/D requirements?

TRIS register setup correctly for PortC.1 to make it an input?

Thanks for the reply.
Yes, a 4Mhz crystal with 22pF caps.
Yes, have tried PullUp/PullDown on hte POL pin for SPI polarity.
Yup, TRIS bits set correctly.

additionally, I have one on a breadboard hooked to an arduino that cycles through all 4 SPI modes, activates the RESET pin on the device to reset it, and sends commands to setup continous conversion mode. (Should make the data ready pin toggle at regular intervals per AD support tech).
Still getting nothing.

I think I either got defective devices or I killed them....