Abstract: An integrated circuit (IC) includes multiple circuits and functions which share multiple internal signal buses, three physical and five logical, according to distributed bus access and control arbitration. The multiple internal signal buses are shared among three tiers of internal circuit functions: a central processing unit and a DMA controller; a DRAM controller and a bus interface unit; and peripheral interface circuits, such as PCMCIA and display controllers. Two of the physical buses correspond to two of the logical buses and are used for communications within the IC. The third physical bus corresponds to three of the logical buses and is used for communications between the IC and circuits external to the IC. Arbitration for accessing and controlling the various signal buses is distributed both within and among the three tiers of internal circuit functions.

Abstract: An educational calculator is provided with means for generating parameters describing a problem to be solved. The user metally solves a problem and inserts the answer to the problem into the calculator. If the user has answered correctly, the calculator lights a green light and displays the problem with the correct answer. If the user answers incorrectly, the calculator displays an error signal. The user is given a second try to answer the problem and, if he fails again, the correct answer is flashed and a new problem is displayed. The calculator keeps track of the number of problems the user has answered correctly. Means are provided within the calculator to permit the calculator to operate in competition with another identical educational calculator. When a cable is connected between two calculators, the calculators are energized to be in the competition mode and only one of the calculators is energized to be a "master" calculator. The other calculator is designated as the "slave.