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ADS8353: CFR Register Data Read Back

Part Number: ADS8353

Dear Sir/madam,

I have a discrepancy in first four bits returned by ADS8353 when performing the readback of CFR register. The bits R15 R14 R13 and R12 are always 0 (confirmed with an oscilloscope) when I issue the CUFF read back command and not 0011 as they should be according the Table 10 of the datasheet. All other bits returned by CFR readback are as I set them with CFR write command. Likewise when I read REFDAC_A and REFDAC_B,  R15 R14 R13 and R12 are as specified in the datasheet Table 10. Also the conversion results I get seems to be in ordered. So ADC is working as expected except for the CFR readback.

My current CRF readback procedure is:

Cfr write:

Set the CFR by sending 1000 and CFR.b10 and CFR.b6 to 1 (all others 0) all in one frame with 48 CLKs.

Cfr read:

Send one empty frame (all zeros) with 48 CLKs. (Frame F in 8.5.3 Data read operation of the datasheet)

Send 0011 and rest 0 to read back CFR.  (Frame F+1 in 8.5.3 Data read operation of the datasheet)

Send one empty frame (all zeros) with 48 CLKs to get the values stored in CFR. (Frame F+2 in 8.5.3 Data read operation of the datasheet)

The CLK speed for a serial communication is currently set to 195kHz. CS between frames is set high for aprox. 1us.


Is this a known error or am I doing something wrong? I tried my procedure with two different ADCs and both exhibit the same behavior.


Best regards,

Rok