Histogram YAxis limits

Hi
I am trying to set a TH1Ds YAxis limits but somehow it does not work.
My code looks like this:

  TCanvas* can = new TCanvas("s","s",1);
  can->Divide(4,4);
  TH1D* h = new TH1D("H","H",n,0,n); 
  h->GetYaxis()->SetLimits(-1.0,1.0);
  for (int i=0;i<16;i++){
    x = ... some vector depending on i...
    for (int j=0;j<n;j++){h->SetBinContent(j+1,x[j]);}
    h->GetYaxis()->SetLimits(-1.0,1.0);
    can->cd(i+1);
    h->DrawCopy();
  }

The limits of the Y axis are not -1.0,1.0 but they only depend on the values i fill into the histogram.

Also I am looking for a way to have the same as TStyle->SetHistTopMargin(double); for the lower Margin. Does this exist?

Thanks in advance

Try:
h->SetMinimum(-1.0);
h->SetMaximum(1.0);