How I can draw the grid lines at intervals with step=1?

[Andres Soto]

Hi
I am trying to draw a step (or staircase) function. My points are all integers. I would like that the grid lines help to identify the limits of each line, but when I draw the grid, it is set each 5 units.
How can I draw the grid lines at intervals with step=1?
Thanks for your help in advance
Regards
Andres 
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