Legato is a function of the controller....not the P5.
I.e. you need a Midi/CV converter that will support Legato playing.
Here´s how it would function :
Press Middle C on the Midikeyboard connected to the interface. The interface will send out a CV corresponding to middle C on its CV output ( Say 2V ). At the Gate output, the interface will send out a positive voltage ( suitable for the P5 ) for as long as you press the midi key.
Keep holding the middle C and simultaneously press another key. If the interface supports legato, it will only update the CV. Not the Gate.
WT - Up north if you didn´t know it......
Just a guy with a bunch of blue things....