RF2 interface protocol
======================

You need to turn an RF carrier on and off. I'm using a carrier of
4.9152MHz, simply because I have an oscillator of that frequency
on my circuit board. Others say that 6MHz is the official frequency.

The oscillator is ANDed with a suitable output from one's PC
(e.g. one could use a parallel port bit) via a TTL gate (such as a
7408), and fed via a 1000pF capacitor in series (it is important to
block the DC power on RF2!) and connected to the RF2 socket.

The RF is modulated using the same bit patterns as the usual IR.
It looks like this:

_ = carrier off
- = carrier on

___------__-_-_-__-__--_-_-_-_-_-_-_-_-_-_-_-_-_--_-_-__-_-_-_-____

   <----- digibox-prefix ----->
                               <-------- 16-data-bits -------->

Each character in the above string is 450us long.

Each data bit is _- to send a '0' and -_ to send a '1', so the above
pattern sends 0070 hex (blue button).

You just need to send the string once to register a keypress.
Leave 300ms between button presses, to ensure all are accepted
(particularly important if you want to press the same button twice).

Here are the codes for the buttons (in hex):

          0=0000
          1=0001
            ...
          9=0009
       Off =000C
       ChUp=0020
     ChDown=0021
       Text=003C
         Up=0058
       Down=0059
       Left=005A
      Right=005B
     Select=005C
        Red=006D
      Green=006E
     Yellow=006F
       Blue=0070
     BoxOff=007D
    Service=007E
        Sky=0080
       Help=0081
     Backup=0083
       Info=00CB
      Guide=00CC
Interactive=00F5