International Business Machines Corporation

Alan F Neel, Ii

Timothy J Louie

James Peter Ward

Margaret E Claffey-Cohen

James Francis Webb

James Ronald Booth

James C Buchanan

Kenneth D Smeltzer

Carl P Cole

Lynn M Oliver

James L Beck

Frank J Schroeder

Donald Richard Andrews

Robert G Hillis

Donald Ward Zegafuse

James P, Ward

Phat T Le

Robert H-c Lin

A parallel port interface for utilization between a first device and a second device designated by a user for transmitting a digital signal from the device to the second device. The parallel port interface includes a switchable driver circuit for transmitting the digital signal, which includes a first circuit for emulating an open collector circuit and a second circuit for emulating a totem pole circuit. The switchable driver circuit is controlled by a logic control circuit that automatically selects either the first circuit or the second circuit for transmitting the digital signal in response to the digital signal and a designation of the second device.

Method and apparatus for controlling parallel port drivers in a data

A system and method is provided for detecting and correcting a lost hardware interrupt generated by an input/output device in a multiple I/O port computer environment. The lost interrupt condition is caused by the simultaneous occurrence of (i) the reading and subsequent resetting of a interrupt request status bit in an I/O port by a device driver and (ii) the setting of the interrupt request status bit by an I/O device attached to the port. Because the interrupt request status bit is reset before it can be read, the device driver fails to see an acknowledgement of the previous data transmission to the I/O device, and the system encounters a deadlock condition. After a normal timeout timer expires the device driver terminates transmission of data and returns a 'cancel or retry' message to the request originator. The present invention prevents a deadlock condition in this situation by providing a second timer in addition to and of significantly less duration than the normal timeout timer. Upon expiration of this additional timer, the device driver, upon satisfying a number of conditions, presumes that an interrupt has been lost, and proceeds to send the next byte of data to the I/O device, thereby preventing a deadlock condition.

Method and system for directing device driver to service multiple

A parallel interface connects a data processor and a printer so that each may transmit information to the other or receive information from the other. The transmitted information from the data processor can be data or status signals. The data or status signals are transmitted over the same eight information lines between the data processor and the printer with a predetermined signal being sent over another line from the data processor to the printer prior to transmission over the eight lines to identify whether the transmitted information is data or status signals. The printer sends status signals to the data processor over the same eight information lines after sending a predetermined signal to the data processor over a further line that it is going to transmit.

Bi-directional parallel printer interface

A method and apparatus are disclosed for electronic collation of sheets of a recording medium, such as paper, printed on one or both sides from electrical signals received at a printer. For printing multiple sets on one side only, the signals are written into a memory in the order in which they are received. The first set may be printed in the desired page order on a recording medium fed through the printer as the signals are received. Additional sets are printed in the same page order by writing the contents of the memory into the printer as many times as necessary as the recording medium is fed through the printer. For printing multiple sets on both sides, the signals representative of every other page are written into the memory and organized into two ordered sequences. One of these sequences contains the electrical signals representative of each of the pages to be printed on one side of the recording medium and the other sequence contains the electrical signals to be printed on the other side of the recording medium. Within each sequence the order of the signals is such that the signals representative of adjacent pages in the order to be printed are adjacent one another in the sequence. Again, the first set may be printed in the desired page order as the signals are received. Each additional set is printed in the desired page order by writing first one sequence and then the other into the printer with one sequence being written in the opposite page order to that in which the signals are received. While the first sequence is being written, the recording medium to be printed is fed through the printer into a last-in-first-out (LIFO) receptacle along a feed path that effectively turns it over. While the second sequence is being written, it is fed from the LIFO sheet receptacle, back through the printer, to an output receptacle.

Method and apparatus for electronic collation

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Boca Raton, FL, United States of America

Alan F Neel, Ii