Common I/O Interface Port for I/O Expansion and Printer Buses
Original Publication Date: 1985-Sep-01
Included in the Prior Art Database: 2005-Feb-19
This article describes an I/O interface technique which enables a single I/O port to be used for an I/O expansion bus, which operates in a standard microprocessor bus mode, and a parallel printer bus, which operates in a mode different from the microprocessor bus mode. Polarity hold latches are utilized to provide both the interface functions required for the I/O expansion and printer buses. An I/O expansion box used for I/O device attachment to a microprocessor is conventionally designed to control a plurality of I/O devices, such as a printer, a plotter and a graphic input device. But there may happen the case where one wants to attach only a printer to the microprocessor. The use of such an I/O box only for the attachment of a printer is very uneconomical.