Sounds like you're talking about splitSeries
in the Simplified XML you would put this inside your <chart>
<option name="charting.layout.splitSeries">False</option>
and in the advanced XML you'd put this inside your HiddenChartFormatter module:
<param name="charting.layout.splitSeries">False</param>
However it's strange that you'd ask this question because False is the default. In other words if you're seeing the split series mode, that means your view already has this configuration in there, and it would be set to True. So maybe you mean something else.
There are some more (very advanced) docs about this at:
http://www.splunk.com/base/Documentation/latest/Developer/AdvChartingConfig-LayoutData
