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Questions about AD7177-2 sample rate

Question asked by haibo2806 on Jul 4, 2017
Latest reply on Jul 6, 2017 by haibo2806

My project need measure 12 channels signal,I use 3 AD7177-2,and 4 channels for each AD7177-2. These 3 AD7177-2 share a same 16Mhz clock,share a SPI BUS, and CS signals connect different GPIOs. I configure AD7177-2 to 200Hz sample rate, thus 50Hz for each channel, in the timer interrupt function( interval is 1.6667ms),  three AD7177-2 's CS signal take turns to set LOW to  read one data. The DOUT/RDY signal is configured as EXIT  function, when DOUT/RDY go LOW, read one date from the selected AD7177-2,then set the selected AD7177-2's CS to HIGH .

My problem is one or more AD7177-2 occasionally stop generating  DOUT/RDY signal, so i can not read data in the EXIT function.

I  tyied another  way,  in the timer interrupt function( interval is 0.8 ms),I read  AD7177-2's state register to check if the RDY bit ==0. If RDY==0, Then set AD7177-2 's CS  to LOW to  read one data, and in the EXIT function, read one date from the selected AD7177-2. The problem is I offen get 5~6 same data, and the data is not continuous,which have Steps,but the input signal is SINE signal.

Please help me how can I read 12 channels's data correctly?