GM implementation assigns Control 5 to Portamento time and 84 to just Portamento.
Does any body knows how to use this pair?, i.e, 84 do this and 5 do that.

On my K25, controller #65 switches the portamento (glide) on/off; 127= on/ 0= off. Controller #5 adjusts the time. It could be that Roland has chosen controller #84 for on/off.

You're right. My question was, how do you use these parameters. Let's say, you sent a control message to switch the glide on/off.
Then you set the time. What time means in this context?.

In fact, Roland lists three Controllers events dealing with portamento: 5 is portamento time. 65 is Portamento, 84 is Portamento control. How are they used?

Mario,
The only portamento controls I have ever had an occasion to use have been on/off and glide time. I don't know about #84 but I can address the other two. I have a switch that I have designated to send #65 Portamento on/ff. When I hit this switch control #65 is sent and the portamento becomes enabled. Since controller #5 is a toggled parameter ( as opposed to variable) on = value of 127, off =0.
I have a slider that has been assigned control #5. Controller #5 is a variable control message, as I move this slider up (open) the glide time is increased, lowered= the length of time between trigger and destination is shortened. When you assign control #5 a value of 0, there should be no portamento effect. When you assign a value of 127, the glide time will be at it's maximum.
Please let me know what you find out about control #84.