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AD9265-FMC-125EBZ SPI Control

Question asked by marcomercuri on Jun 16, 2017
Latest reply on Sep 27, 2017 by PMH

Dear all,


I started interfacing the AD9265-FMC-125EBZ. I read the AD9265 datasheet and I understood that I can control the ADC using either the "SPI mode" or the "External Pin Mode".


Looking at the AD9265-FMC-125EBZ, it seems that some Mode Selection (Table 15 AD9265 datasheet) are set phisically connecting the OEB, PDWN, LVDS, LVDS_RS, and DITHER pins to AGND. I guess this correspond to the "External Pin Mode". The SCLK/DFS, SDIO/DCS, and CSB pins are left floating to be controlled by the FPGA.


I understood that in "External Pin Mode", I have to set CSB to AVDD, and give proper voltage to SCLK/DFS and SDIO/DCS, depending on the modality I want to operate.


It is not clear to me how I can fully operate in "SPI mode". To use the SPI I should indeed set low the CSB and follow the timing diagram. However, after I set the registers, CSB goes high so I guess I enter again in "External Pin Mode". Since the eval board has some pins connected to AGND (OEB, PDWN, LVDS, LVDS_RS, and DITHER), I'm wondering if I lose all the setting I do with the SPI.


For example, let's imagine that through SPI I control OEB, PDWN, LVDS, LVDS_RS, and DITHER. After that, CSB goes to high. I believe I lose my setting since OEB, PDWN, LVDS, LVDS_RS, and DITHER are phisically connected to AGND. Also can I use the SPI if those pins are connected to a potential?


Can you please clarify this point? How can I operate fully in "SPI mode" or in "External Pin Mode"? Can I use both modes?


Thank you very much.


Best Regards,