The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 03, 1985
Filed:
Aug. 12, 1981
James A Brewer, Delray Beach, FL (US);
Lewis C Eggebrecht, Rochester, MN (US);
David A Kummer, Boca Raton, FL (US);
Patricia P McHugh, Boca Raton, FL (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
In a data processing system including a dynamic RAM (14) and a programmable, prioritized direct memory access (DMA) controller (16) having a plurality of channels, the highest priority channel (0) is dedicated to a memory refresh operation. The system clock (P CLK) from the CPU (12) is applied to a divider counter (22) which produces a refresh clock (R CLK) having a period sufficient to generate the minimum number of refresh cycles within the minimum period required to refresh the RAM (14). The refresh clock (R CLK) is used to set a 'D-type' latch (24) whose output, in turn, sets the highest priority DMA channel (0) request line (DREQ0), thereby initiating a memory refresh cycle. The latch (24) is cleared by the DMA acknowledge signal (DACK0) indicating the cycle is completed.