I have a serial interface problem when using ad7656-1 on eval-ad7656-1sdz.
I adjusted the resistors on the ev board to make ad7656-1 be in serial mode, and sending spi_clock/cs signal after the convct_a/b/c pins being toggled.
The problem is that there's no spi slave data on DOUT_A/B/C pins, even though the busy signal is toggled.
And the ad7656-1 ev board works fine in the parallel mode, so I think the board is not broken.
My settings are just like the ones in AN893. I tied DCIN A/B/C and DCEN/DB11/DB12/DB13/RD/WB to the ground, and using internal reference.