If your DDS has a SPI interface with a IO_SYNC pin, the IO_SYNC pin feature can enable writing partial bytes to a multi-byte register. So, that could decrease the write time in those cases.
For example, a 32-bit Frequency Tuning Word (FTW) register is 4 bytes wide, but you only need to program the upper two bytes. Once the instruction byte chooses the FTW register address, the SPI expects all 32 bits (4 bytes) of data to be sent, else the SPI port will get out of sequence. However, if you complete the writing of the upper two bytes of the 4 bytes and then issue an IO_SYNC pulse, it will reset the SPI. So, the next byte will be the instruction byte. Your good to go.
Note, for some older DDSs, the IO_SYNC pin is called the IO_RESET pin, not to be confused with the Master RESET pin.
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