FXO gateway

I am trying to register each port of my FXO gateway to my PBX but I am unsure of the Syntax to make the trunk a registrar instead of a user agent. Any help is appreciated.

What type of Gateway, which version of FreePBX?

Grandstream, I am just looking for the syntax in the trunking to allow the gateway to register to the PBX on each channel.

You didn’t specify a module, here is a link to some documentation for one of their gateways to connect with trixbox, it should be similar or identical configs for FreePBX http://www.grandstream.com/products/gxw_series/gxw410x/documents/gxw410x_interop_trixbox.pdf