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232
Figure 139
Correspondence Between Random Words and Random Bit Stream
The bits of the PRWS are assigned to the generator channels from top to
bottom, as displayed by the Connection Editor.
The PRBS contains the same logical bit sequence just one-directional.
The same principle—only inverted—applies if you are testing a
demultiplexer.
N O T E
Note that the assignment of bits to generator channels is different, if you
apply the PRWS to channels which have been digitally added.
In this case, the system assumes that the word length n is equal to the total
number of channels involved. It assigns the first m bits to the connected
channels and the remaining n – m bits to the added, unconnected channels.
Example
If you had an input port with five terminals and the first two terminals were
connected to two added channels, then terminal 1 would receive the XOR
of bits 1 and 6 and terminal 2 the XOR of bits 2 and 7, as illustrated below:
PRWS bits
6
1
7
2
Figure 140
Bit Assignment to Digitally Added Channels
The benefit of this assignment is explained in "How Can I Create and
Capture a Double-Speed PRWS?" on page 233.
HP 81200 Data Generator/Analyzer Platform User Guide, Revision 2.1
How Do I Set Up a Multiplexer BER Test?
Signal
Bit 1 XORed with bit 6
Bit 2 XORed with bit 7
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