Jump And Set Status Command
Original Publication Date: 1979-Jun-01
Included in the Prior Art Database: 2005-Feb-20
In a computer system, direct memory access circuitry (not shown) is controlled through the use of status information that must be checked by all I/O devices before beginning a data transfer. Once an I/O device gains control, it must alter the status information to prevent any other device from starting a conflicting data transfer operation. In the past, two separate instructions were required to test and alter the status information. Because two separate instructions were required, an I/O device operating on a higher priority level could intervene between the two instructions and initiate a conflicting data transfer operation. A solution to this problem was to use a common microcode routine to test and alter the direct memory access status information.