MATLAB: How to set manually training and test data for training a neural network

neuralnetwork sampling learning

Hello All,
I am making some experiments with mathlab neural network toolbox. Usually to train a neural network i give some training and test data and the net object takes care of dividing the data. However what i need to do is divide the data by myself and set the training and test data explicitly in the net object.
If it is needed some aditional explanation please tell me. Any help would be appreciated.
Thanks.