Working with two CN0326 boards in an application result in corrupt register output.

Hello,

in my application, I need to connect five CN0326 boards to a Raspberry Pi. For the communication, I'm using an I²C to SPI bridge SC18IS602B. I implemented the configuration as described in the Circuit Note (Unipolar Coding, Gain = 1, external reference, continuous conversion mode, update rate f=16.7). I also use a 50 Ohm resistor as channel 1 input and a PT100 as channel 2.

In the evaluation setup, one CN0326 works fine. Then if I use this CN0326 and connect it to the Raspberry Pi via the SC18IS602B, I also get the expected results for the RTD and the pH value. But when I connect a second CN0326 to the bridge, both boards send 1's in the registers.

I tried to figure out what might be the problem by observing the SPI signals. The Chip Enable for both boards is high when no command is sent and only low during a communication (as expected). Also, the SDO signal is high when not active. But I recognized that the SDI signal is low.

Any help is appreciated.

Grit