Teledyne-lecroy CATC Scripting Language Reference Manual Manuel d'utilisateur télécharger pdf (Page 51)

HAPTER

Decoder Primitives

CATC Scripting Language

PeekNBits()

PeekNBits(<bit_count integer>)

Parameter Meaning Default Value Comments

bit_count 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()

Parameter Meaning Default Value Comments

1 2 ... 46 47 48 49 50 51 52 53 54 55 56 57

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Teledyne-lecroy CATC Scripting Language Reference Manual Manuel d'utilisateur Page 51