stm32f103 spi communication with ad7730 random wrong number

[DKari.1]

I am communicating with ad7730 (24bit adc) using atm32f103ZCT6. I try to read one of the registers of the adc but each time I receive a random wrong figure. The strange thing is that while debugging using serial wire (STLINK) everything is perfect and I receive correct number from ad7730. But when I run the board out of the power source I receive wrong data. Any help is appreciated in advance

[TDK]

Use a logic analyzer to see what's happening on the line.

[S.Ma]

Start with oscilloscope. Digital analyser can only be used once you have viewed the analog world. Ringing, slew rate, etc...

[prain]

Try to increase CS (NSS) assertion/de-assertion time (check ad7730 data sheet).

Also try with lower SPI clock.