How to restrict user to input data using datetimepicker and disable manual user input?

I want to restrict the user to only input data using the datetimepicker. Below is the code I am using:

<div class="form-group">
    <label>Start</label>
    <div class="input-group date" id="dtp1">
        <input type="text" id="txtStart" class="form-control" readonly="readonly"/>
        <span class="input-group-addon">
            <span class="glyphicon glyphicon-calendar"></span>
        </span>
    </div>
</div>

$('#dtp1').datetimepicker({
    format: 'DD/MM/YYYY HH:mm A',
    daysOfWeekDisabled: [0, 6]
});

I have tried using the readonly attribute, but this disables both the input and datetimepicker. Is there any way through which I can disable the input field but still allow the user to click on the calendar icon to pick a date?

Use the event.preventDefault() on the keydown event on the input:

<input type="text" id="txtStart" class="form-control" onkeydown="event.preventDefault()">