Introduction to the Example Device

An example device will be presented throughout this document. This will help you to relate to and understand the three key areas of DP4 device handling: device definition, application device handling and OSDI modification. The device we will use will be an imaginary point-of-sale terminal, which we will call "the DP4 Till". The DP4 Till can be broken down into certain areas of functionality which can be mapped to CODs and PODs:

• A slip printer, which can be used to print customer receipts
• A journal printer
• A cash drawer, which is always either open or closed, and can be interrogated for its current state
• An identification number, held in some internal firmware and returned in response to the appropriate request
• A scanner for reading bar codes
• A keyboard for manual input

The sections that follow will use this device to demonstrate some of the principles and methods that you may encounter when accessing a device from a DP4 application.