pro minor

    x=findgen(20)
    y=10.*exp(-x/10.)

    plot,x,y,yrange=[0,10],ystyle=5

    half = 0.5*total(!y.crange)  ; get half of data range
    whalf = 0.5*total(!y.window) ; get half size of plot window
    wsave = !y.window            ; save plot window size

    ; draw bottom half of axis
    !y.window[1] = whalf
    axis,!x.crange[0],YAXIS=0,yrange=[!y.crange[0],half],  $
        ystyle=1,yminor=10
    axis,!x.crange[1],YAXIS=1,yrange=[!y.crange[0],half],  $
        ystyle=1,yminor=10, $
        ytickname=replicate(' ',30)
    !y.window = wsave

    ; draw top half of axis
    !y.window[0] = whalf
    axis,!x.crange[0],YAXIS=0,yrange=[half,!y.crange[1]],  $
        ystyle=1,yminor=3,ytickname=' '
    axis,!x.crange[1],YAXIS=1,yrange=[half,!y.crange[1]],  $
        ystyle=1,yminor=3, $
        ytickname=replicate(' ',30)
    !y.window = wsave

return
end