function out = getwaveform(fid, source, first, last, navg)
%
% This function is used to capture and transfer data from a Tektronix TDS 220 
% digital oscilloscope to a Matlab data structure using an RS-232 (com) port.
% Inputs:
%   fid is pointing to the right serial I/O channel (use the function open_com.m)
%   source is a string containing either 'CH1' or 'CH2'
%   first is the first point to be transferred
%   last is the last point to be transferred
%   navg is the number of waveforms to be averaged (in the scope).
% Ouput Structure:
%   out.time is an array containing the time values for each wavepoint.
%   out.wave is an array containing the waveform data.
%
% Copyright 2002, LJB Development, Inc.
% written by Larry Busse, http://www.ljbdev.com
% Software is provided without warranty.  Use at your own risk.

if nargin < 5, navg =1;end

clear_com(fid);
switch source
case 'CH1', fprintf(fid,'DATA:SOURCE CH1;ENCDG SRI;WIDTH 2');
case 'CH2', fprintf(fid,'DATA:SOURCE CH2;ENCDG SRI;WIDTH 2');
otherwise, err('Problem with source');
end
if navg == 1,
    fprintf(fid,'ACQUIRE:MODE SAMPLE');
else
    fprintf(fid,'ACQUIRE:MODE AVE');
    msg = sprintf('ACQ:NUMAV %d',navg);
    fprintf(fid, msg);
end
msg=sprintf('data:start %d;stop %d;:HEADER OFF',first,last);
fprintf(fid,msg);
%fprintf(fid,'acquire:state stop');
%fprintf(fid,'acquire:state run');
i=0;
while i < navg
    fprintf(fid,'acquire:numacq?');
    line=fgetl(fid);
    i = sscanf(line,'%d');
end

fprintf(fid,'CURVE?');
q=fread(fid,1,'char');   % should be the # character
x=fread(fid,1,'int8');
ss=str2num(char(x));
y=fread(fid,ss,'uchar');
nbytes = str2num(sprintf('%s',y));
nwords = nbytes/2;
data = fread(fid,nwords,'int16');
%[data,count] = fread(fid,10000,'uchar')
%line = fgetl(fid);
%data = sscanf(line,'%d,',inf);
%
clear_com(fid);
qq=sprintf('WFMPRE:%s:NR_PT?',source);fprintf(fid,qq);
npts=fscanf(fid,'%d');
%
qq=sprintf('WFMPRE:%s:YOFF?',source);fprintf(fid,qq);
yoff=fscanf(fid,'%f');
qq=sprintf('WFMPRE:%s:YMULT?',source);fprintf(fid,qq);
ymult=fscanf(fid,'%f');
qq=sprintf('WFMPRE:%s:XINCR?',source);fprintf(fid,qq);
xincr=fscanf(fid,'%f');
qq=sprintf('WFMPRE:%s:PT_OFF?',source);fprintf(fid,qq);
ptoff=fscanf(fid,'%d');
qq=sprintf('WFMPRE:%s:XZERO?',source);fprintf(fid,qq);
t0=fscanf(fid,'%f');
out.time = t0+([0:npts-1] - ptoff)*xincr;
out.data = ymult*(data'-yoff);

function clear_com(fid)
%
% Function used to clear any remaining data from a COMport.
%
% Copyright 2002, LJB Development, Inc.
% written by Larry Busse, http://www.ljbdev.com
% Software is provided without warranty.  Use at your own risk.

n=get(fid,'BytesAvailable');
if n>0
    dummy = fread(fid,n);
end