Abstract: 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.

Abstract: 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.

Abstract: 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.