Agilent Technologies J-BERT N4903, User Manual

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Table 3
Pattern length (standard) Pattern length (alternate) Resolution
> 4 Mbit > 2 Mbit 128 bit
> 8 Mbit > 4 Mbit 256 bit
> 16 Mbit > 8 Mbit 512 bit
How the Serial BERT Generates Memory-Based Patterns
The basic concept of how the Serial BERT generates memory-based
patterns is relatively simple: The Serial BERT has 32Mbits of internal
RAM memory used to store data patterns. The RAM is organized in 64k
of 512-bit blocks.
During test run, the pattern generator reads this memory bit by bit and
generates the corresponding voltage at the output port (1=high, 0=low).
The error detector compares the incoming signal voltage (=data bits)
with the bits in the memory and counts the errors.
The Serial BERT has actually three RAM memory locations where
patterns are stored: in the Pattern Editor memory, in the pattern
generator, and in the error detector. When you modify patterns with the
pattern editor, the patterns in the pattern generator and error detector
are not automatically updated.
For this, you need to write the pattern to the pattern generator and/or
the error detector. There the pattern is saved in the RAM of the
respective module.
Why the Serial BERT Repeats Memory-Based Patterns
To generate output signals, the Serial BERT can send only complete 512-
bit blocks of data. To maintain predictability of the output signal, it is
necessary to send complete patterns. This applies to user patterns,
alternating patterns, memory-based PRBN patterns, mark density
patterns, and zero substitution patterns.
Therefore, when the Serial BERT loads a pattern into its internal
memory, it repeats the pattern as necessary until the pattern reaches a
block boundary. For example, if a 1023-bit pattern is loaded, this is
repeated in the RAM 512 times, and thus occupies 1023 blocks. Or, if a
192-bit pattern is loaded, this is repeated 8 times, and occupies 3 blocks,
as indicated in the following figure. This applies to all memory-based
patterns available to the Serial BERT.
Setting up Patterns
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Agilent J-BERT N4903 High-Performance Serial BERT 31