About SPI Clock timing for readback and write

Question

I want to use AD5781 in very sophisticated, time-critical project and need your help to understand some things 
 There is one line in the datasheet which states, " Maximum SCLK frequency is 35 MHz for write mode and 16 MHz for readback mode. " on page 5 
 
 Here are the queries i have about the SPI Clock, 
 1. When the DAC is initialized, what will be the starting clock speed? 16Mhz or 35Mhz 
 2. If the initial clock frequency is 35 MHz, will it only change to 16 MHz when I use the read command? 
 3. Will the clock continue to run at 35 MHz while writing? unless the read operation is executed. 
 Your help will be appreciated 
 Thank you in advance.

dendalisay · Accepted Answer

Hi kakashi , 
 1.) It does not specify a default or starting clock speed upon initialization in the datasheet but the device itself doesn't set a starting clock speed. The clock frequency is set by the controller device. The 35 MHz (write) and 16 MHz (read) are maximum limits. 
 2.) The maximum SCLK frequency for the AD5781 is 35 MHz during write operations and 16 MHz during readback operations​. The clock speed should be adjusted to comply. 
 3.)The clock can continuously run at 35 MHz (max) during write operations. Reduce to 16 MHz for read operations only. These figures mentioned in the datasheet are maximum limits for write/readback operations and are not starting speeds perse, but rather the upper limits that the device can reliably operate at for each type of operation. 
 Br, 
 Den)

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About SPI Clock timing for readback and write