futaba digi servos

[stevo]

hi i currently run a s3154 on my gaui as a tail servo with the gaui giro
does any one now if this servo will take digital

also have a s 3153 on my blade 400 with stock giro
in the book it says the giro puts out a digital signal of 275mhz can these
futaba servos take this digital signal or do i run them in analog mode

dont really understand as i thought a digi servo was a digi servo
but having read a few things its all about pulse rates
if its run in analog mode does this make much difference to the speed