how to extract rules from neural network?

i want to extract classification rules from the neural network , which maps input of the network with its the output.

How can i extract this type of rules?

1) is there any tool to extract these? if yes then which tool is it? or,

2) we need to write code for that? if yes then how can i write that? or,

3) we need to form the rules manually?

please suggest me something.....

input will be in binary or numeric form .....