add option for splitting data into upper and lower 16 bits (#2428)

* TYPO in comment

* ENH - allow for splitting lower and higher 16 bit

fileio/ft_read_event.m

@@ -585,7 +585,7 @@
  end
 
  try
- % read the trigger codes from the STIM channel, usefull for (pseudo) continuous data
+ % read the trigger codes from the STIM channel, useful for (pseudo) continuous data
  % this splits the trigger channel into the lowers and highest 16 bits,
  % corresponding with the front and back panel of the electronics cabinet at the Donders Centre
  [backpanel, frontpanel] = read_ctf_trigger(filename);

fileio/private/read_trigger.m

@@ -40,7 +40,7 @@
 begsample = ft_getopt(varargin, 'begsample' );
 endsample = ft_getopt(varargin, 'endsample' );
 chanindx = ft_getopt(varargin, 'chanindx' ); % specify -1 in case you don't want to detect triggers
-detectflank = ft_getopt(varargin, 'detectflank' ); % can be up, updiff, down, downdiff, both, any, biton, bitoff
+detectflank = ft_getopt(varargin, 'detectflank' ); % can be up, updiff, down, downdiff, both, any, biton, bitoff, optionally appended with _split16bit
 denoise = ft_getopt(varargin, 'denoise', true );
 trigshift = ft_getopt(varargin, 'trigshift', 0); % causes the value of the trigger to be obtained from a sample that is shifted N samples away from the actual flank
 trigpadding = ft_getopt(varargin, 'trigpadding', true );
@@ -255,9 +255,24 @@
  end
 end
 
+label = hdr.label(chanindx);
+if contains(detectflank, 'split16bit')
+ % split the trigger channel into lower and higher (bitshifted) trigger channels. 
+ % this is the same functionality as read_ctf_trigger, consider merging
+ dat_high = fix(dat / 2^16);
+ dat_low = double(bitand(uint32(dat), 2^16-1));
+ dat = [dat_low; dat_high];
+
+ label = cat(1, cellfun(@sprintf, repmat({'%s_low16bit'},numel(label),1), label, 'UniformOutput', false), ...
+ cellfun(@sprintf, repmat({'%s_high16bit'},numel(label),1), label, 'UniformOutput', false));
+
+ tok = tokenize(detectflank, '_');
+ detectflank = tok{1};
+end
+
 for i = 1:size(dat,1)
  % process each trigger channel independently
- channel = hdr.label{chanindx(i)};
+ channel = label{i};
  trig = dat(i,:);
 
  if trigpadding