ACCOUNTING SYSTEM WITH A SCIENCE SYSTEM.

摘要

A computer includes a video subsystem with a CRT display, a video controller and a video memory for CRT data which requires access by the controller and a CPU. The subsystem monitors activity of the CRT screen display and the video controller and anytime CRT screen display is not required regardless of the time of occurrence, the CPU is allowed to have access to the video memory during the cycle or cycles in which such inactivity of display occurs. A guaranteed minimum number of cycles is assured for access of the video memory by the CPU during a high speed mode, but in addition arbitration allows CPU access to occur during non-display times so that the CPU can acquire more cycles if necessary. In a low speed mode, arbitration occurs both during display and non-display periods so that the CPU can acquire memory cycles on an as needed basis.