Parallel I/O options for 8085-based systems

Realtime applications of any microprocessor necessitate interfacing to a large variety of peripheral devices. Various interfacing techniques are discussed. Examples are given in which Intel's 8085 is taken as the typical microprocessor. The I/O transfers considered fall into two categories: memory-mapped transfers and I/O-mapped transfers. Both synchronous and asynchronous types are dealt with. Bit masking and interrupt techniques were used for asynchronous memory-mapped I/O transfer.Also included are multiplexed channel transfers and interrupt transfers. The former are treated as a special class of I/O transfer. The latter are useful in applications where it cannot be predicted when data will arrive for transfer to the microprocessor. Unlike other types of transfer, interrupt transfers are initiated by the I/O devices and not by the microprocessor. They are subdivided into software- and hardware-polled transfers. Examples are given of daisychain and search ring transfers.