DVDO VP50 PRO - Manual (Page 62)

A Burst Pair Sequence usually looks as follows:
Lead in Burst Pair Data Burst Pairs Lead Out Burst Pair
The Lead In Burst pair can be thought of as the hello or wake up burst. It tells the
receiver to start listening (or rather looking) very closely as what is coming. It is usually
of different timing duration than the Burst Pairs in the data part. Technically it is also
used to set the receivers AGC level, a factor related to how much the receiver will
amplify the IR light it sees.
The Lead Out burst pair marks the end of the message and usually has a long OFF
time period to guarantee that two IR messages can’t be sent too close together. It may
actually be incorporated as part of the last data bit if the ON period is what carries the
information (that is, the off time is constant in the data portion and the On time varies
between two values). Once again, Sony does exactly that.
Remember all data in the IR Hex display is in Hex and to properly interpret these
values you must convert them to decimal. Two values should be considered equal if they
are within about 10% of each other. They don’t have to be exactly the same.
[Digression to convert a 4 digit Hex "WXYZ" number to decimal, the following
formula will work W*4096+X*256+Y*16+Z. W,X,Y,Z represent HEX digits in the
range 0-15 where a=10, b=11,c=12,d=13,e=14,f=15. A hex value of 0067 is therefore
16*6+7=103)].
If you understand all of what has been discussed so far you have based the basics
of Binary Signaling 101. Go take a breather.
Before we look at some actual IR codes and their detailed formats, we should
understand why there might be two burst sequences in the code and not always just one.
The first burst sequence is the Once sequence. It is sent if you tap the button on the
Pronto which has learned this code. The second burst sequence is called the Repeat
sequence. It is sent repeatedly as long as you hold the key on the Pronto down. If you
have used an IR remote you already know that all buttons do not "repeat". The two
sequences do not have to be the same. In many cases they are, in others they are not. This
is generally manufacturer dependent.
62