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:
Oct. 01, 1996
Filed:
Aug. 16, 1993
Michael D McCormack, Robbinsdale, MN (US);
Romuald M Jurewicz, St. Louis Park, MN (US);
Dannis R Johnson, Savage, MN (US);
Thermo King Corporation, Minneapolis, MN (US);
Abstract
A method of securely controlling direct memory access (DMA) in a microprocessor controlled system having a CPU on a CPU board which has an address/data bus connector for selectively connecting an expansion board to the CPU board, and a random access memory (RAM) on the CPU board having a specific address range which is accessible by a DMA device on the expansion board when the CPU board relinquishes control of the address/data bus to the DMA device in response to a bus access request. The method includes the steps of providing a plurality of logic signals, including a first logic signal having logic levels which indicate whether or not the CPU board is in control of the address/data bus, providing memory select signals for selecting different memory address ranges which are true in response to different Boolean equations each comprising predetermined combinations of predetermined logic signals, and including the first signal in the Boolean equation of at least one of the memory select signals, such that the at least one memory select signal can only be driven to a true level when the logic level of the first logic signal indicates that the CPU board is in control of the address/data bus. The method may be used to control DMA in a refrigeration related process or system.