A Digital option has a predefined payoff. For most options the payoff of an option is unknown and is only known upon exerciseof the option, which the payoff for a call option being the asset price on exericise less the strike price of the options. In contrast a digital option has the payoff defined when the option is issued.
The payoff of a Digital option is preset to be either a cash amount (as in a Cash-or-Nothing option) or a unit of the underlying option (ie an Asset-or-Nothing option). For example a Cash-or-Nothing option on a stock would either payoff zero or a fixed cash at expiry, similary an Asset-or-Nothing option would either payoff zero or a fixed number of stocks.
For an Asset-or-Nothing Digital there are no inputs to the pricing model over the standard black scholes inputs , for Cash-or-Nothing Digital there is only the input of the cash amount.
DerivativeOne features a free valuation tool for Asset-or-Nothing and Cash-or-Nothing digitals.