Teledyne LeCroy LeCroy Analyzers File Based Decoding Manual - Manual (Page 49)

File-based Decoding User Manual Chapter 11: Primitives
LeCroy Corporation
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PeekNBits()
PeekNBits(integer>)
Support
Supported by all LeCroy analyzers.
Return value
None.
Comments
Reads bit_count bits from the data source. The difference between PeekNBits and
NextNBits
is that PeekNBits does not advance the global bit offset. PeekNBits can
be used to make decisions about how to parse the next fields without affecting
subsequent calls to NextNBits. If PeekNBits is called without a prior call to
GetNBits
, the result is undefined. Note that bits are indexed starting at bit 0.
Example
raw = 'F0F0';# 1111000011110000 binary
result1 = GetNBits ( raw, 2, 4 );
result2 = PeekNBits(5);
result3 = NextNBits(2);
Trace ( "result1 = ", result1, " result2 = ", result2, " result3
= ", result3 );
This generates this Trace output:
result1 = C result2 = 7 result3 = 0
In the call to GetNBits: starting at bit 2, reads 4 bits (1100), and returns the value 0xC.
In the call to PeekNBits: starting at bit 6, reads 5 bits (00111), and returns the value 0x7.
In the call to NextNBits: starting at bit 6, reads 2 bits (00), and returns the value 0x0.
Parameter Meaning
Default
Value Comments
bit_count integer