Agilent Technologies N4906B Serial BERT User Manual page 27

User Patterns
Agilent N4906B Serial BERT, User's Guide, October 2005
For example, a user pattern that is 256,001 bit bit long would have to
be loaded into the RAM 512 times to reach the 512-bit boundary. Such
a pattern would occupy more than 128 Mbits in the RAM.
The Serial BERT handles such patterns by rounding them off to the
nearest length that would fit in the memory. For the above example,
the length would be rounded off to 256,000 bits. This rounding-off
factor is known as the pattern's resolution. The following table lists all
pattern resolutions.
Pattern length Pattern length
(standard) (alternate)
≤ 64 kbit ≤ 32 kbit
> 64 kbit > 32 kbit
> 128 kbit > 64 kbit
> 256 kbit > 128 kbit
> 512 kbit > 256 kbit
> 1 Mbit > 512 kbit
> 2 Mbit > 1 Mbit
> 4 Mbit > 2 Mbit
> 8 Mbit > 4 Mbit
> 16 Mbit > 8 Mbit
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 32 Mbits 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.
Setting up Patterns
Resolution
1 bit
2 bit
4 bit
8 bit
16 bit
32 bit
64 bit
128 bit
256 bit
512 bit
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