Teledyne-lecroy Protocol Analyzers File-Based Decoding User Manual Instrukcja Użytkownika Pobierz pdf (Strona 48)

Chapter 11: Primitives File-based Decoding User Manual

42 LeCroy Corporation

PeekNBits()

PeekNBits(<bit_count integer>)

Parameter Meaning

Default

Value Comments

bit_count in

teger

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

e 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. No

te that bits are indexed starting at bit 0.

Example

raw = 'F0F0';# 1111000011110000 binary

result1 = GetNBits ( raw, 2, 4 );

result2 = PeekNBits(5);

result3 = NextNBits(2);

This results in:

result1 == C

result2 == 7

result3 == 0

A call to GetNBits, starting at bit 2, reads 4 bits (1100), and returns the value 0xC.

A call to PeekNBits, starting at bit 6, reads 5 bits (00111), and returns the value 0x7.

A call to NextNBits, starting at bit 6, reads 2 bits (00), and returns the value 0x0.

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