Edit in JSFiddle

var myApp = angular.module('myApp', []);


myApp.controller('Ctrl1', myController);

myController.$inject = ['$scope']

function myController($scope) {
    $scope.foo = "setted in ctrl1";
    $scope.talkToCtrl2 = function () {
		//Implement this function
    }
};

myApp.controller('Ctrl2', myController2);

myController2.$inject = ['$scope']

function myController2($scope) {
    $scope.foo = "setted in ctrl2";

};
<div>
    <div ng-controller="Ctrl1">
        <input type="text" ng-model="foo" />
        <input type="button" value="Talk to Ctrl2" ng-click="talkToCtrl2()" />
    </div>
    <div ng-controller="Ctrl2">{{foo}}</div>
</div>

              

External resources loaded into this fiddle: