Teledyne LeCroy USB Script Decode Manual - Manual (Page 54)

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C HAPTER 12
CATC Scripting Language for USB Decoder Primitives
PeekNBits()
PeekNBits(integer>)
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 will generate 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.
Pending()
Pending()
Parameter Meaning Default Value Comments
bit_count integer
Parameter Meaning Default Value Comments