User Frame Z Value into Register

I am trying to use the Variable $MNUFRAME[1,1].POSITION.Z to read the z value of my User Frame into a Register. I know this syntax works when setting user frames via a CM file, but if I write "R[1] = $MNUFRAME[1,1].POSITION.Z" into a TP program, I get an error "Parameter not Found". Any ideas?

Thanks in Advance for any help.

Quote from Fabian Munoz

do

PR[a]=UF[b]

R[c]=PR[a,3]

R[c] has the value of Z

I should have added that I am attempting to do this in BG logic, So I can't execute the first line of that code.

Quote from Sergei Troizky

There is no known method to refer a frame component in BG logic.

Execute the 1st line in the main program.

Thanks, this is my current method, was just looking for something "cleaner".