ASP .NET and JavaScript --passing values from textbox to script

I am working in C# and JavaScript with an 'onload' event and a JavaScript time.  I am able to start and stop the timer  in the asp page with buttons.  I am able to start the time on the page load with onload = InitializeTimer().   However, I would like to be able to set the time value dynamically.  In other words, I would like to have a textbox where I could enter 20 followed by pressing the start button which would then call InitializeTimer() but pass a value to set 'secs' from 'secs=10' to the passed value.  If I can get this process to work I would then just have the onload event pass in a number as well 'InitializeTimer(10)' for it to work.  Any ideas how this could work.

<SCRIPT language="JavaScript">
<!--
var secs
var timerID = null
var timerRunning = false
var delay = 1000
var runtime

function InitializeTimer()
{
    // Set the length of the timer, in seconds
   
    secs = 10
    StopTheTimer()
    StartTheTimer()
}

function StopTheTimer()
{
    if(timerRunning)
        clearTimeout(timerID)
    timerRunning = false
}

function StartTheTimer()
{
 
   
    if (secs==0)
    {
        StopTheTimer()
        InitializeTimer()
        //document.frmManageQueue.submit();
        __doPostBack("AUTOREFRESH","");
       
    }
    else
    {
        self.status = secs
        secs = secs - 1
        timerRunning = true
        timerID = self.setTimeout("StartTheTimer()", delay)
       
    }
}
//-->
</SCRIPT>

Thanks