Layout - unused pins

I am going to lay out a minimal board for the ADuCM350, primarily focusing on the AFE and SPI sections.  My AFE will be measuring a high-impedance sensor.  For minimizing coupled noise, what are your recommendations as far as un-used pins (i.e. leaving them floating vs. grounded, etc.)?  Also, for unused sections (e.g. the cap-touch sensor, the LCD, the USB, which have their own labeled power and ground pins) what do you recommend as far as connecting those sections'  power and ground pins and/or capacitors across them?

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  • Ah, okay, I see.  It turns out that digging through the digital isolators more thoroughly, I found a better one.  The ADuM241 works as low as 1.8V, is 4-channel and can do 150 Mbps, so it's perfect.

    Regarding the different ground pins on the ADuCM350 (I got confused ... it's the VCCM_DIG and VCCM_ANA that are connected on chip), if I take the shunt jumper off of LK10 and measure across the two pins, I see 15 ohms (with no daughter cards connected, and no connection between the eval board and chassis enclosure).  Any guesses where that 15 ohms come from?  Inside the ADuCM350?  On the eval board?

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  • Ah, okay, I see.  It turns out that digging through the digital isolators more thoroughly, I found a better one.  The ADuM241 works as low as 1.8V, is 4-channel and can do 150 Mbps, so it's perfect.

    Regarding the different ground pins on the ADuCM350 (I got confused ... it's the VCCM_DIG and VCCM_ANA that are connected on chip), if I take the shunt jumper off of LK10 and measure across the two pins, I see 15 ohms (with no daughter cards connected, and no connection between the eval board and chassis enclosure).  Any guesses where that 15 ohms come from?  Inside the ADuCM350?  On the eval board?

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