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Event Latching in an Asynchronous Environment

IP.com Disclosure Number: IPCOM000036152D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Bealkowski, R: AUTHOR [+4]

Abstract

This article describes a circuit arrangement in a personal computer (PC) system which latches the universal peripheral interface (UPI) interrupting event external to the UPI to insure recognition by the host.

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Event Latching in an Asynchronous Environment

This article describes a circuit arrangement in a personal computer (PC) system which latches the universal peripheral interface (UPI) interrupting event external to the UPI to insure recognition by the host.

In a PC system where a UPI, which is a microcomputer, is used to provide the interface to the keyboard and mouse devices, the UPI receives data from the keyboard or mouse and presents the data to the host for processing. When the UPI presents this data it signals the host through an interrupt. The UPI is connected to the host's interrupt controllers through UPI output pins. The UPI indicates an interrupt by setting the appropriate output pin to a value of one. Through the interrupt controllers, the host is notified of an interrupt from the UPI.

The PC system operates in a level-sensitive interrupt environment. This means that a device raises and holds its interrupt line until it is serviced. This mechanism allows for interrupt levels to be shared between devices. When signaling an interrupt to the host the UPI manipulates its output pins under program control. The action of operating the output bits under program control creates an asynchronous environment with respect to the host. Not only does the UPI set an interrupt under program control, it also clears the interrupt bit under program control. The end of the interrupt condition is when the host reads the data that the UPI is presenting.

However, the UPI is not able to clear the output bit to the interrupt controllers at the same exact instant that the host reads the data. The UPI cannot clear the condition because it must execute a number of instructions before it can determ...