Status and command function extension for industry standard printer interfaces

摘要

A computer system is connected to a printer via a parallel interface, for point-of-sale (POS) applications employing one or more different paper sources, such as, continuous tape, document insertion, and sheet validation. A detector is associated with each paper source to sense a paper empty or out condition. The printer has an addressable latch that enables a choice of one or more of these detectors for connection through to a single status line within the parallel printer interface. The computer CPU can access the addressable latch prior to any printing so that the presence of an appropriate type of paper in its appropriate print position in the printer can be checked or tested utilizing an industry standard parallel printer interface, such as, the widely employed Centronics interface.