DVDO VP50 PRO - Manual (Page 61)

having them equal. We might choose 48,24 for the "1" and 24,24 for the "0". In fact this
is what Sony has done in its IR remotes. [Note: If you work through the numbers you will
find that Sony IR signaling uses a sequence of 1200 microseconds of light followed by
600 microseconds of no light to represent a "1"; and a sequence of 600 microseconds of
light followed by 600 microseconds of no light to represent a "0"]. In general all IR
equipment is forgiving and operates with in a timing tolerance of +/- 10%.
A full IR key code as encoded in the ProntoEdit Hex display contains three
discrete parts.
Preamble Burst Pair Sequence 1 Burst Pair Sequence 2
Either one of the burst pair sequences is optional so we will actually have three
different patterns of IR encoding.
Preamble
Preamble
Preamble Burst Pair Sequence 1
Burst Pair Sequence 1
Burst Pair Sequence 2 Burst Pair Sequence 2
The preamble does not contain Burst Pairs but rather four (4) hexadecimal (HEX,
base 16) numbers, each of which has a precise meaning. I will only discuss them in the
context of Learned IR codes. Each Hex number consists of 4 digits.
The first number is always a zero (0000) it indicates that the IR pattern is raw
data, which means it was learned.
The second number is the frequency of the IR carrier in terms of the Pronto
internal clock. The following formula where N represents the decimal value of this hex
number will give you the frequency of the carrier in Kilohertz: Frequency = 1000000/(N
* .241246)
A Sony remote will usually have a value for N of 103 (this shows as 67 Hex).
Doing the arithmetic we have Freq=1000000/(103*. 241246)= 40,244 or approximately
40,000 cycles per second (well within a tolerance of 40,000 +/- 10%)
The third number is the number of Burst Pairs in Burst Pair Sequence #1. Each
Burst pair consists of two 4 digit Hex numbers representing the On and Off time of that
burst (single binary Bit).
The fourth number is the number of Burst Pairs in Burst Pair Sequence #2.
Burst Pair Sequence #1 starts at word 5 if it is present and is immediately
followed by the digits of Burst Pair Sequence #2 if it is present (word 4>0000). If
Sequence #1 is missing (word 3=0000), then Burst Sequence Number 2 starts at word 5.
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