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Address Decoding in Restricted Address Space

IP.com Disclosure Number: IPCOM000038895D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01

Publishing Venue

IBM

Related People

Authors:
Oliver, LM Ware, DW [+details]

Abstract

A battery back-up, realtime, clock-calendar chip, which requires sixty- four addresses in a personal computer, can be operated with only two addresses in the personal computer while the chip still functions as if there are sixty-four addresses. This allows the chip to reside in a restricted address space. Only two addresses in an IBM PC are used by a Motorola 146818 realtime clock chip 2, which requires sixty-four addresses and is connected to the IBM PC through a decode logic 3. These two addresses may be two of the sixteen addresses assigned to the IBM Game Adapter Card, such as addresses 0203H and 0205H, for example. The IBM Game Adapter Card uses only two of the sixteen addresses, and it does not use 0203H and 0205H, for example.