! = start command (lets the RS232 receiving device know what follows is a command. Its a delimiter between any other noise on the line or maybe if it is still listening for a CR/etc, it knows this is new information.
7=Destination Unit (dvd, receiver, etc). As the command structure is essentially the same across all their devices, in case you had a rs232 chain or something, this number lets the dvd player know to listen and not the receiver. {1 is receiver, 2 is DVD, 7 is Bluray}.
PWR = Command (tell the unit which command it is about execute.
00= Parameter (now that it knows to start (!) and that the command is designed for it (7) and which command it should use (PWR) then 00 tell the device what to do with that command. The contrast would be 01 for on and 02 for toggle.
Integra/Onkyo also use a CR as a end of character. My control system sends it automatically. What are you using?
As another example, take the colored buttons for Bluray.
