>> pardon me, I'm newbie
With 230 posts over 6 months, I think you're not a newbie anymore
When you want to control a/v equipment, you can do it many different ways. Most just use a gc100/tira/irtrans and send i/r codes. But you can also use gsd. Look at the Denon AVC rs232 receiver. it is a gsd device.
internally to pluto none of that matters. when it's time to turn the receiver on, it sends an on command to the receiver. if the Denon receiver's command line is 'generic_serial_device' (like the denon's is), then gsd will expect the i/r table to contain ruby code snippets that it uses to send commands over rs232. if the denon receiver has no command line and doesn't implement dce, but is a child of a gc100, then the on command goes to the gc100, which assumes the i/r data contains a code in pronto format.
The link he provided shows the Marantz rs232 protocol. To add a device template for it, choose wizard/devices/a/v equipment. add device, choose manufactur: marantz, category: receiver 'add' new model and choose 'gsd'. Fill out the wizard, be sure teh marantz is added to the a/v page. Then go to wizard/devices/generic serial devices. click 'edit ruby codes' for the marantz, and in each of the boxes supply the commands marantz provided in the document. this is exactly teh same like with the denon rs232.
Of course you can mix and match--soem a/v equipment rs232, some is infrared.