[Premium-Rx] muting the rf-590?

[ehertz]

Hi all, I am looking to integrate my RF-590H into my ham shack.  i see there is a mute input on the rear terminal strip which I would like to actuate from my TR relay.  The manual doesn't explicitly say how to actuate this externally, but does mention an internal mute that needs +5V TTL input. 

I am hoping (praying) that the external mute function has some kind of pull up resistor and all I need to do is ground it.  Can anyone confirm? Otherwise, I will have to find a way to supply +5V to it when the TR relay fires.  If 5V is infact needed, perhaps it can be borrowed from some other connector signal supplied by the 590? 

Any and all (or no) info appreciated
thanks
Eugene