How to reverse the sequence of axis Y ??

Hello R-users!

My (simple?) doubt: How to reverse the sequence of axis Y ??

the diagram below illustrate my idea...

(default)
   |
   |
.  |
.  |
.  |
3  |
2  |
1  |
0  +----------------------------
   0 1 2 3 ...



like I want...
 
0  |
1  |
2  |
3  |
.  |
.  |
.  |
   |
   +----------------------------
   0 1 2 3 ...


thanks in advance


klebyn