Principles of Data Transfer

Abstract

In order to transfer data reliably to and from external devices in a bus or ‘partyline’ structure such as a microprocessor system, it is essential to provide the processor with the facility to select one device register to communicate with. All other register and storage areas must remain in the off state to prevent mutilation of the data. The selection is arranged by allocating a unique address (usually 16 bits) or device code (usually 8 bits) to each register in the interface. Logic is provided at each interface which ensures that any device code can energise only the required register and will not select any other.