You can set keyframes with Stepped interpolation or change keyframes to use Stepped interpolation.
To set keyframes with Stepped interpolation:
 
                  Key Controls A. Stepped interpolation selected in the Type menu
To change the interpolation of a keyframe to Stepped:
 
                  FCurves window (detail) in Classic Mode A. Stepped interpolation type selected for the keyframe selection B. Step and Step Next mode
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License