Non-Return to Zero (NRZ) signals use two voltage levels (high and low) to represent logic one and logic zero values. Traditional oscilloscopes can capture and view these waveforms but do not have the capability to decode waveforms into their digital equivalents. Oscilloscopes with XDEV custom functionality can now decode these waveforms.

In Figure 1, a block of NRZ data is acquired as Function F1 and the parameter TIE@lv (Time Interval Error) is applied as parameter P1. The Virtual Clock capability of TIE reports the underlying bitrate as 2.488 Gb/s, which corresponds to this OC-48 datastream. Function F2 allows for a user-defined Matlab script to automatically decode each waveform as shown in Figure 2. The algorithm reads the base frequency from the TIE parameter to locate boundaries of each unit interval. As the algorithm processes each waveform edge, it appends the logic value into a buffer of datastream values. When the loop completes, the digitallydecoded waveform and its statistics are displayed as well as recorded to a file. This process will repeat for each acquisition allowing rapid in-line waveform conversion.

`clear bitstream; % erase previous bitstream values `

WformOut = WformIn1 - mean(WformIn1); % offset the waveform to place the mean value

at zero

comclient off % needed for Matlab rev 6.5 - delete this line if using any other Matlab revision

h = actxserver('LeCroy.WaveMasterApplication'); % establish ActiveX control between

the scope and Matlab

xincr = h.Math.F1.Out.Result.HorizontalPerStep; % sample resolution

basefreq = double(get(h.Measure.P1.Operator.BaseFrequency,'Value')); % TIE frequency

determination

baseper = 1/basefreq;

samplesperbit = ceil(baseper/xincr);

n = find(diff(WformOut>0)); % locate position of edges on the NRZ data

numberofedges = length(n);

bitcounter = 0; % initialize a bit counter

virtualclockposition = n(1); %

numones = 0; % keep track of total number of ones identified

numzeros = 0; % keep track of total number of zeros identified

for i=1:(numberofedges-1)

virtualclockposition = n(i); % set virtual clock to coincide with NRZ edge transitions

bitswide = round((n(i+1)-n(i))/samplesperbit); % determine how many bits occur

between edges

for j=1:bitswide % for example if there are two zeros in a row between edges,

execute this loop twice to check both bits

bitcounter = bitcounter + 1; % keep track of how many bits have been checked

so far

if (WformOut(virtualclockposition + ceil(samplesperbit/2)) > 0) % the amplitude is high, this bit is a One

bitstream(bitcounter) = 1; % log the value of this bit as a zero or one for

future reference

numones = numones + 1; % increment the total number of identified One values

else

bitstream(bitcounter) = 0; % the amplitude low, this bit is a Zero

numzeros = numzeros + 1; % increment the total number of identified Zero

values

end

end

end

%% SAVE BITSTREAM TO A FILE

disp(' ')

bitstream = char(bitstream+48) % convert values to ascii

outputfile = 'bitstream.txt';

fid = fopen(outputfile, 'w');

fwrite(fid,bitstream,'char');

fclose(fid);

fprintf('Stats: %d Bits, %d Ones, %d Zeros, output saved to %s

',

length(bitstream), numones, numzeros, outputfile);