In this design, I have five devices sharing the same SPI clock and data lines; three LTC2630 DACs, one ADF4372 PLL and one ADF4002 PLO. Each of course has its own enable line. I have noted that the evaluation boards for ADF4372 and ADF4002 include series resistors in line with each device's clock, data and enable pins. However, I have not seen reference to them in the datasheets for the devices. What is the purpose of these resistances and are they really needed?
Does the fact that multiple devices exist on the same lines effect the need for these resistances?