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ADXL357B SPI reads return all 1s

I have an ADXL357B connected to the McBSP of a TI C2000 DSP.  The SPI bus is shared with 2 other devices, running at 5MHz.  Any read I try to do of an ADXL357 register, the MISO pin stays high the entire time and I get all 1s as the register contents.

I connected up a USB logic analyzer and captured the below trace.  This is a read of register 0x01, the R/W bit you can see is set for a read.  I expected the MISO data on those last 8 clock pulses to be 0x1D.  This is just one example, it doesn't matter which register I read, I always get all 1s coming back as the MISO stays high the entire duration of the SPI transaction.  Since this part autodetects I2C or SPI, is there some pin timing that I need to meet in order to switch into SPI mode?  

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