Identify the Buy/Sell Signal according to the SuperTrend value

I can calculate the ATR according to the time period i.e. Time Period = 10. Also taken the multiplier = 3.
Got the formula to calculate the Up and Down value.

Up = ((high + low) / 2) + (multiplier x ATR)
Down = ((high + low) / 2) - (multiplier x ATR)

Now, when to generate the Buy / Sell signal, according to the above calculation. As Up value is always greater than Close Value and Down Value is always less than Close value.

What to do next to generate the Buy / Sell signal?