What are the advantages and disadvantages of serial and parallel mode?

Serial mode offers the advantage of fewer traces on the pc board, and fewer pins on the devices. Parallel offers the advantage of transferring 8 data bits per I/O clock cycle, but at the disadvantage of many more pins required on the devices.

On some of the DDS devices (AD9852/54/58) the parallel port offers the advantage of addressing single bytes in the device register set, whereas the serial port requires all of the bytes of a multibyte register to be loaded at one time.

Overall, the parallel mode offers the advantage of faster loading of the registers, but with the disadvantage of requiring more interconnect traces. The serial mode offers simplicity, but with less speed.

In some cases, an application may require a data update rate which can be achieved while using the parallel mode, but which could not be accomplished while using the serial mode due to its slower update rate.