The E-Series device do not have built-in retriggerable hardware. You will need to use the counter to generate the scan clock. Here are a few links that I found on NIs web site by doing a search for retriggerable.
http://sine.ni.com/apps/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3E8B756A4E034080020E74861&p_node=DZ52335&p_submitted=N&p_rank=&p_answer=&p_source=External
http://sine.ni.com/apps/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3F09F56A4E034080020E74861&p_node=DZ52335&p_submitted=N&p_rank=&p_answer=&p_source=External
I hope this helps out.
Joshua