Abstract: A microprocessor system includes a microprocessor, a memory, and one or more direct memory access controllers, all connected to a common system bus which includes a system address bus and a system data bus. At least one of the direct memory access controllers is shared by a plurality of subsystem device controllers which may control peripheral devices having diverse characteristics. The microprocessor is limited in its instruction repertoire and may control peripheral devices only by means of an input and an output instruction. The shared direct memory access controller includes no circuitry which is specifically for controlling only a single type of peripheral device, the device dependent logic being located in subsystem device controllers. Data transfers may take place directly between the memory and, through the shared direct memory access controller, any selected one of the peripheral devices.

Abstract: Circuitry external of a microprocessor determines priority between different peripheral devices requesting interrupts to generate a restart vector and a signal granting priority to one of the interrupt-requesting devices. The peripheral device loads its status and address into two addressable registers connected to a common system bus. The restart vector is loaded into the instruction register of the microprocessor. The microprocessor treats the restart vector as an instruction to store the contents of the program counter in memory and loads certain bits of the restart vector into the program counter. These bits represent the starting address of a subroutine of eight instructions for analyzing the interrupt. An interrupt is recognized and the status and identification of the interrupting device is stored in a single instruction cycle. On the next instruction cycle the first instruction of the interrupt analysis routine may begin.